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6.4.5.11 Audit Log Reference

The following sections provide a reference to MySQL Enterprise Audit elements:

To install the audit log tables and functions, use the instructions provided in Section 6.4.5.2, 鈥淚nstalling or Uninstalling MySQL Enterprise Audit鈥?/a>. Unless those objects are installed, the audit_log plugin operates in legacy mode. See Section 6.4.5.10, 鈥淟egacy Mode Audit Log Filtering鈥?/a>.

Audit Log Tables

MySQL Enterprise Audit uses tables in the mysql system database for persistent storage of filter and user account data. The tables can be accessed only by users who have privileges for that database. The tables use the InnoDB storage engine.

If these tables are missing, the audit_log plugin operates in legacy mode. See Section 6.4.5.10, 鈥淟egacy Mode Audit Log Filtering鈥?/a>.

The audit_log_filter table stores filter definitions. The table has these columns:

The audit_log_user table stores user account information. The table has these columns:

  • USER

    The user name part of an account. For an account user1@localhost, the USER part is user1.

  • HOST

    The host name part of an account. For an account user1@localhost, the HOST part is localhost.

  • FILTERNAME

    The name of the filter assigned to the account. The filter name associates the account with a filter defined in the audit_log_filter table.

Audit Log Functions

This section describes, for each audit log function, its purpose, calling sequence, and return value. For information about the conditions under which these functions can be invoked, see Section 6.4.5.7, 鈥淎udit Log Filtering鈥?/a>.

Each audit log function returns a string that indicates whether the operation succeeded. OK indicates success. ERROR: message indicates failure.

As of MySQL 8.0.19, audit log functions convert string arguments to utf8mb4 and string return values are utf8mb4 strings. Prior to MySQL 8.0.19, audit log functions treat string arguments as binary strings (which means they do not distinguish lettercase), and string return values are binary strings.

If an audit log function is invoked from within the mysql client, binary string results display using hexadecimal notation, depending on the value of the --binary-as-hex. For more information about that option, see Section 4.5.1, 鈥渕ysql 鈥?The MySQL Command-Line Client鈥?/a>.

These audit log functions are available:

  • audit_log_encryption_password_get([keyring_id])

    This function fetches an audit log encryption password from the MySQL keyring, which must be enabled or an error occurs. Any keyring component or plugin can be used; for instructions, see Section 6.4.4, 鈥淭he MySQL Keyring鈥?/a>.

    With no argument, the function retrieves the current encryption password as a binary string. An argument may be given to specify which audit log encryption password to retrieve. The argument must be the keyring ID of the current password or an archived password.

    For additional information about audit log encryption, see Encrypting Audit Log Files.

    Arguments:

    keyring_id: As of MySQL 8.0.17, this optional argument indicates the keyring ID of the password to retrieve. The maximum permitted length is 766 bytes. If omitted, the function retrieves the current password.

    Prior to MySQL 8.0.17, no argument is permitted. The function always retrieves the current password.

    Return value:

    The password string for success (up to 766 bytes), or NULL and an error for failure.

    Example:

    Retrieve the current password:

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    mysql> SELECT audit_log_encryption_password_get(); +-------------------------------------+ | audit_log_encryption_password_get() | +-------------------------------------+ | secret | +-------------------------------------+

    To retrieve a password by ID, you can determine which audit log keyring IDs exist by querying the Performance Schema keyring_keys table:

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    mysql> SELECT KEY_ID FROM performance_schema.keyring_keys WHERE KEY_ID LIKE 'audit_log%' ORDER BY KEY_ID; +-----------------------------+ | KEY_ID | +-----------------------------+ | audit_log-20190415T152248-1 | | audit_log-20190415T153507-1 | | audit_log-20190416T125122-1 | | audit_log-20190416T141608-1 | +-----------------------------+ mysql> SELECT audit_log_encryption_password_get('audit_log-20190416T125122-1'); +------------------------------------------------------------------+ | audit_log_encryption_password_get('audit_log-20190416T125122-1') | +------------------------------------------------------------------+ | segreto | +------------------------------------------------------------------+
  • audit_log_encryption_password_set(password)

    Sets the current audit log encryption password to the argument and stores the password in the MySQL keyring. As of MySQL 8.0.19, the password is stored as a utf8mb4 string. Prior to MySQL 8.0.19, the password is stored in binary form.

    If encryption is enabled, this function performs a log file rotation operation that renames the current log file, and begins a new log file encrypted with the password. The keyring must be enabled or an error occurs. Any keyring component or plugin can be used; for instructions, see Section 6.4.4, 鈥淭he MySQL Keyring鈥?/a>.

    For additional information about audit log encryption, see Encrypting Audit Log Files.

    Arguments:

    password: The password string. The maximum permitted length is 766 bytes.

    Return value:

    1 for success, 0 for failure.

    Example:

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    mysql> SELECT audit_log_encryption_password_set(password); +---------------------------------------------+ | audit_log_encryption_password_set(password) | +---------------------------------------------+ | 1 | +---------------------------------------------+
  • audit_log_filter_flush()

    Calling any of the other filtering functions affects operational audit log filtering immediately and updates the audit log tables. If instead you modify the contents of those tables directly using statements such as INSERT, UPDATE, and DELETE, the changes do not affect filtering immediately. To flush your changes and make them operational, call audit_log_filter_flush().

    Warning

    audit_log_filter_flush() should be used only after modifying the audit tables directly, to force reloading all filters. Otherwise, this function should be avoided. It is, in effect, a simplified version of unloading and reloading the audit_log plugin with UNINSTALL PLUGIN plus INSTALL PLUGIN.

    audit_log_filter_flush() affects all current sessions and detaches them from their previous filters. Current sessions are no longer logged unless they disconnect and reconnect, or execute a change-user operation.

    If this function fails, an error message is returned and the audit log is disabled until the next successful call to audit_log_filter_flush().

    Arguments:

    None.

    Return value:

    A string that indicates whether the operation succeeded. OK indicates success. ERROR: message indicates failure.

    Example:

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    mysql> SELECT audit_log_filter_flush(); +--------------------------+ | audit_log_filter_flush() | +--------------------------+ | OK | +--------------------------+
  • audit_log_filter_remove_filter(filter_name)

    Given a filter name, removes the filter from the current set of filters. It is not an error for the filter not to exist.

    If a removed filter is assigned to any user accounts, those users stop being filtered (they are removed from the audit_log_user table). Termination of filtering includes any current sessions for those users: They are detached from the filter and no longer logged.

    Arguments:

    • filter_name: A string that specifies the filter name.

    Return value:

    A string that indicates whether the operation succeeded. OK indicates success. ERROR: message indicates failure.

    Example:

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    mysql> SELECT audit_log_filter_remove_filter('SomeFilter'); +----------------------------------------------+ | audit_log_filter_remove_filter('SomeFilter') | +----------------------------------------------+ | OK | +----------------------------------------------+
  • audit_log_filter_remove_user(user_name)

    Given a user account name, cause the user to be no longer assigned to a filter. It is not an error if the user has no filter assigned. Filtering of current sessions for the user remains unaffected. New connections for the user are filtered using the default account filter if there is one, and are not logged otherwise.

    If the name is %, the function removes the default account filter that is used for any user account that has no explicitly assigned filter.

    Arguments:

    • user_name: The user account name as a string in user_name@host_name format, or % to represent the default account.

    Return value:

    A string that indicates whether the operation succeeded. OK indicates success. ERROR: message indicates failure.

    Example:

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    mysql> SELECT audit_log_filter_remove_user('user1@localhost'); +-------------------------------------------------+ | audit_log_filter_remove_user('user1@localhost') | +-------------------------------------------------+ | OK | +-------------------------------------------------+
  • audit_log_filter_set_filter(filter_name, definition)

    Given a filter name and definition, adds the filter to the current set of filters. If the filter already exists and is used by any current sessions, those sessions are detached from the filter and are no longer logged. This occurs because the new filter definition has a new filter ID that differs from its previous ID.

    Arguments:

    • filter_name: A string that specifies the filter name.

    • definition: A JSON value that specifies the filter definition.

    Return value:

    A string that indicates whether the operation succeeded. OK indicates success. ERROR: message indicates failure.

    Example:

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    mysql> SET @f = '{ "filter": { "log": false } }'; mysql> SELECT audit_log_filter_set_filter('SomeFilter', @f); +-----------------------------------------------+ | audit_log_filter_set_filter('SomeFilter', @f) | +-----------------------------------------------+ | OK | +-----------------------------------------------+
  • audit_log_filter_set_user(user_name, filter_name)

    Given a user account name and a filter name, assigns the filter to the user. A user can be assigned only one filter, so if the user was already assigned a filter, the assignment is replaced. Filtering of current sessions for the user remains unaffected. New connections are filtered using the new filter.

    As a special case, the name % represents the default account. The filter is used for connections from any user account that has no explicitly assigned filter.

    Arguments:

    • user_name: The user account name as a string in user_name@host_name format, or % to represent the default account.

    • filter_name: A string that specifies the filter name.

    Return value:

    A string that indicates whether the operation succeeded. OK indicates success. ERROR: message indicates failure.

    Example:

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    mysql> SELECT audit_log_filter_set_user('user1@localhost', 'SomeFilter'); +------------------------------------------------------------+ | audit_log_filter_set_user('user1@localhost', 'SomeFilter') | +------------------------------------------------------------+ | OK | +------------------------------------------------------------+
  • audit_log_read([arg])

    Reads the audit log and returns a JSON string result. If the audit log format is not JSON, an error occurs.

    With no argument or a JSON hash argument, audit_log_read() reads events from the audit log and returns a JSON string containing an array of audit events. Items in the hash argument influence how reading occurs, as described later. Each element in the returned array is an event represented as a JSON hash, with the exception that the last element may be a JSON null value to indicate no following events are available to read.

    With an argument consisting of a JSON null value, audit_log_read() closes the current read sequence.

    For additional details about the audit log-reading process, see Section 6.4.5.6, 鈥淩eading Audit Log Files鈥?/a>.

    Arguments:

    To obtain a bookmark for the most recently written event, call audit_log_read_bookmark().

    arg: The argument is optional. If omitted, the function reads events from the current position. If present, the argument can be a JSON null value to close the read sequence, or a JSON hash. Within a hash argument, items are optional and control aspects of the read operation such as the position at which to begin reading or how many events to read. The following items are significant (other items are ignored):

    • start: The position within the audit log of the first event to read. The position is given as a timestamp and the read starts from the first event that occurs on or after the timestamp value. The start item has this format, where value is a literal timestamp value:

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      "start": { "timestamp": "value" }

      The start item is permitted as of MySQL 8.0.22.

    • timestamp, id: The position within the audit log of the first event to read. The timestamp and id items together comprise a bookmark that uniquely identify a particular event. If an audit_log_read() argument includes either item, it must include both to completely specify a position or an error occurs.

    • max_array_length: The maximum number of events to read from the log. If this item is omitted, the default is to read to the end of the log or until the read buffer is full, whichever comes first.

    To specify a starting position to audit_log_read(), pass a hash argument that includes either a start item or a bookmark consisting of timestamp and id items. If a hash argument includes both a start item and a bookmark, an error occurs.

    If a hash argument specifies no starting position, reading continues from the current position.

    If a timestamp value includes no time part, a time part of 00:00:00 is assumed.

    Return value:

    If the call succeeds, the return value is a JSON string containing an array of audit events, or a JSON null value if that was passed as the argument to close the read sequence. If the call fails, the return value is NULL and an error occurs.

    Example:

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    mysql> SELECT audit_log_read(audit_log_read_bookmark()); +-----------------------------------------------------------------------+ | audit_log_read(audit_log_read_bookmark()) | +-----------------------------------------------------------------------+ | [ {"timestamp":"2020-05-18 22:41:24","id":0,"class":"connection", ... | +-----------------------------------------------------------------------+ mysql> SELECT audit_log_read('null'); +------------------------+ | audit_log_read('null') | +------------------------+ | null | +------------------------+

    Notes:

    Prior to MySQL 8.0.19, string return values are binary JSON strings. For information about converting such values to nonbinary strings, see Section 6.4.5.6, 鈥淩eading Audit Log Files鈥?/a>.

  • audit_log_read_bookmark()

    Returns a JSON string representing a bookmark for the most recently written audit log event. If the audit log format is not JSON, an error occurs.

    The bookmark is a JSON hash with timestamp and id items that uniquely identify the position of an event within the audit log. It is suitable for passing to audit_log_read() to indicate to that function the position at which to begin reading.

    For additional details about the audit log-reading process, see Section 6.4.5.6, 鈥淩eading Audit Log Files鈥?/a>.

    Arguments:

    None.

    Return value:

    A JSON string containing a bookmark for success, or NULL and an error for failure.

    Example:

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    mysql> SELECT audit_log_read_bookmark(); +-------------------------------------------------+ | audit_log_read_bookmark() | +-------------------------------------------------+ | { "timestamp": "2019-10-03 21:03:44", "id": 0 } | +-------------------------------------------------+

    Notes:

    Prior to MySQL 8.0.19, string return values are binary JSON strings. For information about converting such values to nonbinary strings, see Section 6.4.5.6, 鈥淩eading Audit Log Files鈥?/a>.

  • audit_log_rotate()

    Arguments:

    None.

    Return value:

    The renamed file name.

    Example:

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    mysql> SELECT audit_log_rotate();

    Using audit_log_rotate() requires the AUDIT_ADMIN privilege.

Audit Log Option and Variable Reference

Table 6.44 Audit Log Option and Variable Reference

Name Cmd-Line Option File System Var Status Var Var Scope Dynamic
audit-log Yes Yes
audit_log_buffer_size Yes Yes Yes Global No
audit_log_compression Yes Yes Yes Global No
audit_log_connection_policy Yes Yes Yes Global Yes
audit_log_current_session Yes Both No
Audit_log_current_size Yes Global No
audit_log_disable Yes Yes Yes Global Yes
audit_log_encryption Yes Yes Yes Global No
Audit_log_event_max_drop_size Yes Global No
Audit_log_events Yes Global No
Audit_log_events_filtered Yes Global No
Audit_log_events_lost Yes Global No
Audit_log_events_written Yes Global No
audit_log_exclude_accounts Yes Yes Yes Global Yes
audit_log_file Yes Yes Yes Global No
audit_log_filter_id Yes Both No
audit_log_flush Yes Global Yes
audit_log_format Yes Yes Yes Global No
audit_log_include_accounts Yes Yes Yes Global Yes
audit_log_max_size Yes Yes Yes Global Yes
audit_log_password_history_keep_days Yes Yes Yes Global Yes
audit_log_policy Yes Yes Yes Global No
audit_log_prune_seconds Yes Yes Yes Global Yes
audit_log_read_buffer_size Yes Yes Yes Varies Varies
audit_log_rotate_on_size Yes Yes Yes Global Yes
audit_log_statement_policy Yes Yes Yes Global Yes
audit_log_strategy Yes Yes Yes Global No
Audit_log_total_size Yes Global No
Audit_log_write_waits Yes Global No
Name Cmd-Line Option File System Var Status Var Var Scope Dynamic

Audit Log Options and Variables

This section describes the command options and system variables that configure operation of MySQL Enterprise Audit. If values specified at startup time are incorrect, the audit_log plugin may fail to initialize properly and the server does not load it. In this case, the server may also produce error messages for other audit log settings because it does not recognize them.

To configure activation of the audit log plugin, use this option:

If the audit log plugin is enabled, it exposes several system variables that permit control over logging:

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mysql> SHOW VARIABLES LIKE 'audit_log%'; +--------------------------------------+--------------+ | Variable_name | Value | +--------------------------------------+--------------+ | audit_log_buffer_size | 1048576 | | audit_log_compression | NONE | | audit_log_connection_policy | ALL | | audit_log_current_session | OFF | | audit_log_disable | OFF | | audit_log_encryption | NONE | | audit_log_exclude_accounts | | | audit_log_file | audit.log | | audit_log_filter_id | 0 | | audit_log_flush | OFF | | audit_log_format | NEW | | audit_log_format_unix_timestamp | OFF | | audit_log_include_accounts | | | audit_log_max_size | 0 | | audit_log_password_history_keep_days | 0 | | audit_log_policy | ALL | | audit_log_prune_seconds | 0 | | audit_log_read_buffer_size | 32768 | | audit_log_rotate_on_size | 0 | | audit_log_statement_policy | ALL | | audit_log_strategy | ASYNCHRONOUS | +--------------------------------------+--------------+

You can set any of these variables at server startup, and some of them at runtime. Those that are available only for legacy mode audit log filtering are so noted.

Audit Log Status Variables

If the audit log plugin is enabled, it exposes several status variables that provide operational information. These variables are available for legacy mode audit filtering and JSON mode audit filtering.


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Excerpts from this Manual

17.1.6.4 Binary Logging Options and Variables

You can use the mysqld options and system variables that are described in this section to affect the operation of the binary log as well as to control which statements are written to the binary log. For additional information about the binary log, see Section 5.4.4, 鈥淭he Binary Log鈥?/a>. For additional information about using MySQL server options and system variables, see Section 5.1.7, 鈥淪erver Command Options鈥?/a>, and Section 5.1.8, 鈥淪erver System Variables鈥?/a>.

Startup Options Used with Binary Logging

The following list describes startup options for enabling and configuring the binary log. System variables used with binary logging are discussed later in this section.

  • --binlog-row-event-max-size=N

    Command-Line Format --binlog-row-event-max-size=#
    System Variable (鈮?8.0.14) binlog_row_event_max_size
    Scope (鈮?8.0.14) Global
    Dynamic (鈮?8.0.14) No
    SET_VAR Hint Applies (鈮?8.0.14) No
    Type Integer
    Default Value 8192
    Minimum Value 256
    Maximum Value (64-bit platforms) 18446744073709551615
    Maximum Value (32-bit platforms) 4294967295
    Unit bytes

    When row-based binary logging is used, this setting is a soft limit on the maximum size of a row-based binary log event, in bytes. Where possible, rows stored in the binary log are grouped into events with a size not exceeding the value of this setting. If an event cannot be split, the maximum size can be exceeded. The value must be (or else gets rounded down to) a multiple of 256. The default is 8192 bytes.

  • --log-bin[=base_name]

    Command-Line Format --log-bin=file_name
    Type File name

    Specifies the base name to use for binary log files. With binary logging enabled, the server logs all statements that change data to the binary log, which is used for backup and replication. The binary log is a sequence of files with a base name and numeric extension. The --log-bin option value is the base name for the log sequence. The server creates binary log files in sequence by adding a numeric suffix to the base name.

    If you do not supply the --log-bin option, MySQL uses binlog as the default base name for the binary log files. For compatibility with earlier releases, if you supply the --log-bin option with no string or with an empty string, the base name defaults to host_name-bin, using the name of the host machine.

    The default location for binary log files is the data directory. You can use the --log-bin option to specify an alternative location, by adding a leading absolute path name to the base name to specify a different directory. When the server reads an entry from the binary log index file, which tracks the binary log files that have been used, it checks whether the entry contains a relative path. If it does, the relative part of the path is replaced with the absolute path set using the --log-bin option. An absolute path recorded in the binary log index file remains unchanged; in such a case, the index file must be edited manually to enable a new path or paths to be used. The binary log file base name and any specified path are available as the log_bin_basename system variable.

    In earlier MySQL versions, binary logging was disabled by default, and was enabled if you specified the --log-bin option. From MySQL 8.0, binary logging is enabled by default, whether or not you specify the --log-bin option. The exception is if you use mysqld to initialize the data directory manually by invoking it with the --initialize or --initialize-insecure option, when binary logging is disabled by default. It is possible to enable binary logging in this case by specifying the --log-bin option. When binary logging is enabled, the log_bin system variable, which shows the status of binary logging on the server, is set to ON.

    To disable binary logging, you can specify the --skip-log-bin or --disable-log-bin option at startup. If either of these options is specified and --log-bin is also specified, the option specified later takes precedence. When binary logging is disabled, the log_bin system variable is set to OFF.

    When GTIDs are in use on the server, if you disable binary logging when restarting the server after an abnormal shutdown, some GTIDs are likely to be lost, causing replication to fail. In a normal shutdown, the set of GTIDs from the current binary log file is saved in the mysql.gtid_executed table. Following an abnormal shutdown where this did not happen, during recovery the GTIDs are added to the table from the binary log file, provided that binary logging is still enabled. If binary logging is disabled for the server restart, the server cannot access the binary log file to recover the GTIDs, so replication cannot be started. Binary logging can be disabled safely after a normal shutdown.

    The --log-slave-updates and --slave-preserve-commit-order options require binary logging. If you disable binary logging, either omit these options, or specify --log-slave-updates=OFF and --skip-slave-preserve-commit-order. MySQL disables these options by default when --skip-log-bin or --disable-log-bin is specified. If you specify --log-slave-updates or --slave-preserve-commit-order together with --skip-log-bin or --disable-log-bin, a warning or error message is issued.

    In MySQL 5.7, a server ID had to be specified when binary logging was enabled, or the server would not start. In MySQL 8.0, the server_id system variable is set to 1 by default. The server can now be started with this default server ID when binary logging is enabled, but an informational message is issued if you do not specify a server ID explicitly by setting the server_id system variable. For servers that are used in a replication topology, you must specify a unique nonzero server ID for each server.

    For information on the format and management of the binary log, see Section 5.4.4, 鈥淭he Binary Log鈥?/a>.

  • --log-bin-index[=file_name]

    Command-Line Format --log-bin-index=file_name
    System Variable log_bin_index
    Scope Global
    Dynamic No
    SET_VAR Hint Applies No
    Type File name

    The name for the binary log index file, which contains the names of the binary log files. By default, it has the same location and base name as the value specified for the binary log files using the --log-bin option, plus the extension .index. If you do not specify --log-bin, the default binary log index file name is binlog.index. If you specify --log-bin option with no string or an empty string, the default binary log index file name is host_name-bin.index, using the name of the host machine.

    For information on the format and management of the binary log, see Section 5.4.4, 鈥淭he Binary Log鈥?/a>.

Statement selection options.  The options in the following list affect which statements are written to the binary log, and thus sent by a replication source server to its replicas. There are also options for replicas that control which statements received from the source should be executed or ignored. For details, see Section 17.1.6.3, 鈥淩eplica Server Options and Variables鈥?/a>.

  • --binlog-do-db=db_name

    Command-Line Format --binlog-do-db=name
    Type String

    This option affects binary logging in a manner similar to the way that --replicate-do-db affects replication.

    The effects of this option depend on whether the statement-based or row-based logging format is in use, in the same way that the effects of --replicate-do-db depend on whether statement-based or row-based replication is in use. You should keep in mind that the format used to log a given statement may not necessarily be the same as that indicated by the value of binlog_format. For example, DDL statements such as CREATE TABLE and ALTER TABLE are always logged as statements, without regard to the logging format in effect, so the following statement-based rules for --binlog-do-db always apply in determining whether or not the statement is logged.

    Statement-based logging.  Only those statements are written to the binary log where the default database (that is, the one selected by USE) is db_name. To specify more than one database, use this option multiple times, once for each database; however, doing so does not cause cross-database statements such as UPDATE some_db.some_table SET foo='bar' to be logged while a different database (or no database) is selected.

    Warning

    To specify multiple databases you must use multiple instances of this option. Because database names can contain commas, the list is treated as the name of a single database if you supply a comma-separated list.

    An example of what does not work as you might expect when using statement-based logging: If the server is started with --binlog-do-db=sales and you issue the following statements, the UPDATE statement is not logged:

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    USE prices; UPDATE sales.january SET amount=amount+1000;

    The main reason for this 鈥?span class="quote">just check the default database鈥?/span> behavior is that it is difficult from the statement alone to know whether it should be replicated (for example, if you are using multiple-table DELETE statements or multiple-table UPDATE statements that act across multiple databases). It is also faster to check only the default database rather than all databases if there is no need.

    Another case which may not be self-evident occurs when a given database is replicated even though it was not specified when setting the option. If the server is started with --binlog-do-db=sales, the following UPDATE statement is logged even though prices was not included when setting --binlog-do-db:

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    USE sales; UPDATE prices.discounts SET percentage = percentage + 10;

    Because sales is the default database when the UPDATE statement is issued, the UPDATE is logged.

    Row-based logging.  Logging is restricted to database db_name. Only changes to tables belonging to db_name are logged; the default database has no effect on this. Suppose that the server is started with --binlog-do-db=sales and row-based logging is in effect, and then the following statements are executed:

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    USE prices; UPDATE sales.february SET amount=amount+100;

    The changes to the february table in the sales database are logged in accordance with the UPDATE statement; this occurs whether or not the USE statement was issued. However, when using the row-based logging format and --binlog-do-db=sales, changes made by the following UPDATE are not logged:

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    USE prices; UPDATE prices.march SET amount=amount-25;

    Even if the USE prices statement were changed to USE sales, the UPDATE statement's effects would still not be written to the binary log.

    Another important difference in --binlog-do-db handling for statement-based logging as opposed to the row-based logging occurs with regard to statements that refer to multiple databases. Suppose that the server is started with --binlog-do-db=db1, and the following statements are executed:

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    USE db1; UPDATE db1.table1, db2.table2 SET db1.table1.col1 = 10, db2.table2.col2 = 20;

    If you are using statement-based logging, the updates to both tables are written to the binary log. However, when using the row-based format, only the changes to table1 are logged; table2 is in a different database, so it is not changed by the UPDATE. Now suppose that, instead of the USE db1 statement, a USE db4 statement had been used:

    Press CTRL+C to copy
    USE db4; UPDATE db1.table1, db2.table2 SET db1.table1.col1 = 10, db2.table2.col2 = 20;

    In this case, the UPDATE statement is not written to the binary log when using statement-based logging. However, when using row-based logging, the change to table1 is logged, but not that to table2鈥攊n other words, only changes to tables in the database named by --binlog-do-db are logged, and the choice of default database has no effect on this behavior.

  • --binlog-ignore-db=db_name

    Command-Line Format --binlog-ignore-db=name
    Type String

    This option affects binary logging in a manner similar to the way that --replicate-ignore-db affects replication.

    The effects of this option depend on whether the statement-based or row-based logging format is in use, in the same way that the effects of --replicate-ignore-db depend on whether statement-based or row-based replication is in use. You should keep in mind that the format used to log a given statement may not necessarily be the same as that indicated by the value of binlog_format. For example, DDL statements such as CREATE TABLE and ALTER TABLE are always logged as statements, without regard to the logging format in effect, so the following statement-based rules for --binlog-ignore-db always apply in determining whether or not the statement is logged.

    Statement-based logging.  Tells the server to not log any statement where the default database (that is, the one selected by USE) is db_name.

    When there is no default database, no --binlog-ignore-db options are applied, and such statements are always logged. (Bug #11829838, Bug #60188)

    Row-based format.  Tells the server not to log updates to any tables in the database db_name. The current database has no effect.

    When using statement-based logging, the following example does not work as you might expect. Suppose that the server is started with --binlog-ignore-db=sales and you issue the following statements:

    Press CTRL+C to copy
    USE prices; UPDATE sales.january SET amount=amount+1000;

    The UPDATE statement is logged in such a case because --binlog-ignore-db applies only to the default database (determined by the USE statement). Because the sales database was specified explicitly in the statement, the statement has not been filtered. However, when using row-based logging, the UPDATE statement's effects are not written to the binary log, which means that no changes to the sales.january table are logged; in this instance, --binlog-ignore-db=sales causes all changes made to tables in the source's copy of the sales database to be ignored for purposes of binary logging.

    To specify more than one database to ignore, use this option multiple times, once for each database. Because database names can contain commas, the list is treated as the name of a single database if you supply a comma-separated list.

    You should not use this option if you are using cross-database updates and you do not want these updates to be logged.

Checksum options.  MySQL supports reading and writing of binary log checksums. These are enabled using the two options listed here:

  • --binlog-checksum={NONE|CRC32}

    Command-Line Format --binlog-checksum=type
    Type String
    Default Value CRC32
    Valid Values

    NONE

    CRC32

    Enabling this option causes the source to write checksums for events written to the binary log. Set to NONE to disable, or the name of the algorithm to be used for generating checksums; currently, only CRC32 checksums are supported, and CRC32 is the default. You cannot change the setting for this option within a transaction.

To control reading of checksums by the replica (from the relay log), use the --slave-sql-verify-checksum option.

Testing and debugging options.  The following binary log options are used in replication testing and debugging. They are not intended for use in normal operations.

  • --max-binlog-dump-events=N

    Command-Line Format --max-binlog-dump-events=#
    Type Integer
    Default Value 0

    This option is used internally by the MySQL test suite for replication testing and debugging.

  • --sporadic-binlog-dump-fail

    Command-Line Format --sporadic-binlog-dump-fail[={OFF|ON}]
    Type Boolean
    Default Value OFF

    This option is used internally by the MySQL test suite for replication testing and debugging.

System Variables Used with Binary Logging

The following list describes system variables for controlling binary logging. They can be set at server startup and some of them can be changed at runtime using SET. Server options used to control binary logging are listed earlier in this section.


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17.1.6.5 Global Transaction ID System Variables

The MySQL Server system variables described in this section are used to monitor and control Global Transaction Identifiers (GTIDs). For additional information, see Section 17.1.3, 鈥淩eplication with Global Transaction Identifiers鈥?/a>.

  • binlog_gtid_simple_recovery

    Command-Line Format --binlog-gtid-simple-recovery[={OFF|ON}]
    System Variable binlog_gtid_simple_recovery
    Scope Global
    Dynamic No
    SET_VAR Hint Applies No
    Type Boolean
    Default Value ON

    This variable controls how binary log files are iterated during the search for GTIDs when MySQL starts or restarts.

    When binlog_gtid_simple_recovery=TRUE, which is the default in MySQL 8.0, the values of gtid_executed and gtid_purged are computed at startup based on the values of Previous_gtids_log_event in the most recent and oldest binary log files. For a description of the computation, see The gtid_purged System Variable. This setting accesses only two binary log files during server restart. If all binary logs on the server were generated using MySQL 5.7.8 or later, binlog_gtid_simple_recovery=TRUE can always safely be used.

    If any binary logs from MySQL 5.7.7 or older are present on the server (for example, following an upgrade of an older server to MySQL 8.0), with binlog_gtid_simple_recovery=TRUE, gtid_executed and gtid_purged might be initialized incorrectly in the following two situations:

    • The newest binary log was generated by MySQL 5.7.5 or earlier, and gtid_mode was ON for some binary logs but OFF for the newest binary log.

    • A SET @@GLOBAL.gtid_purged statement was issued on MySQL 5.7.7 or earlier, and the binary log that was active at the time of the SET @@GLOBAL.gtid_purged statement has not yet been purged.

    If an incorrect GTID set is computed in either situation, it remains incorrect even if the server is later restarted with binlog_gtid_simple_recovery=FALSE. If either of these situations apply or might apply on the server, set binlog_gtid_simple_recovery=FALSE before starting or restarting the server.

    When binlog_gtid_simple_recovery=FALSE is set, the method of computing gtid_executed and gtid_purged as described in The gtid_purged System Variable is changed to iterate the binary log files as follows:

    • Instead of using the value of Previous_gtids_log_event and GTID log events from the newest binary log file, the computation for gtid_executed iterates from the newest binary log file, and uses the value of Previous_gtids_log_event and any GTID log events from the first binary log file where it finds a Previous_gtids_log_event value. If the server's most recent binary log files do not have GTID log events, for example if gtid_mode=ON was used but the server was later changed to gtid_mode=OFF, this process can take a long time.

    • Instead of using the value of Previous_gtids_log_event from the oldest binary log file, the computation for gtid_purged iterates from the oldest binary log file, and uses the value of Previous_gtids_log_event from the first binary log file where it finds either a nonempty Previous_gtids_log_event value, or at least one GTID log event (indicating that the use of GTIDs starts at that point). If the server's older binary log files do not have GTID log events, for example if gtid_mode=ON was only set recently on the server, this process can take a long time.

  • enforce_gtid_consistency

    Command-Line Format --enforce-gtid-consistency[=value]
    System Variable enforce_gtid_consistency
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Enumeration
    Default Value OFF
    Valid Values

    OFF

    ON

    WARN

    Depending on the value of this variable, the server enforces GTID consistency by allowing execution of only statements that can be safely logged using a GTID. You must set this variable to ON before enabling GTID based replication.

    The values that enforce_gtid_consistency can be configured to are:

    • OFF: all transactions are allowed to violate GTID consistency.

    • ON: no transaction is allowed to violate GTID consistency.

    • WARN: all transactions are allowed to violate GTID consistency, but a warning is generated in this case.

    --enforce-gtid-consistency only takes effect if binary logging takes place for a statement. If binary logging is disabled on the server, or if statements are not written to the binary log because they are removed by a filter, GTID consistency is not checked or enforced for the statements that are not logged.

    Only statements that can be logged using GTID safe statements can be logged when enforce_gtid_consistency is set to ON, so the operations listed here cannot be used with this option:

    • CREATE TEMPORARY TABLE or DROP TEMPORARY TABLE statements inside transactions.

    • Transactions or statements that update both transactional and nontransactional tables. There is an exception that nontransactional DML is allowed in the same transaction or in the same statement as transactional DML, if all nontransactional tables are temporary.

    • CREATE TABLE ... SELECT statements, prior to MySQL 8.0.21. From MySQL 8.0.21, CREATE TABLE ... SELECT statements are allowed for storage engines that support atomic DDL.

    For more information, see Section 17.1.3.7, 鈥淩estrictions on Replication with GTIDs鈥?/a>.

    Prior to MySQL 5.7 and in early releases in that release series, the boolean enforce_gtid_consistency defaulted to OFF. To maintain compatibility with these earlier releases, the enumeration defaults to OFF, and setting --enforce-gtid-consistency without a value is interpreted as setting the value to ON. The variable also has multiple textual aliases for the values: 0=OFF=FALSE, 1=ON=TRUE,2=WARN. This differs from other enumeration types but maintains compatibility with the boolean type used in previous releases. These changes impact on what is returned by the variable. Using SELECT @@ENFORCE_GTID_CONSISTENCY, SHOW VARIABLES LIKE 'ENFORCE_GTID_CONSISTENCY', and SELECT * FROM INFORMATION_SCHEMA.VARIABLES WHERE 'VARIABLE_NAME' = 'ENFORCE_GTID_CONSISTENCY', all return the textual form, not the numeric form. This is an incompatible change, since @@ENFORCE_GTID_CONSISTENCY returns the numeric form for booleans but returns the textual form for SHOW and the Information Schema.

  • gtid_executed

    System Variable gtid_executed
    Scope Global
    Dynamic No
    SET_VAR Hint Applies No
    Type String
    Unit set of GTIDs

    When used with global scope, this variable contains a representation of the set of all transactions executed on the server and GTIDs that have been set by a SET gtid_purged statement. This is the same as the value of the Executed_Gtid_Set column in the output of SHOW MASTER STATUS and SHOW REPLICA STATUS. The value of this variable is a GTID set, see GTID Sets for more information.

    When the server starts, @@GLOBAL.gtid_executed is initialized. See binlog_gtid_simple_recovery for more information on how binary logs are iterated to populate gtid_executed. GTIDs are then added to the set as transactions are executed, or if any SET gtid_purged statement is executed.

    The set of transactions that can be found in the binary logs at any given time is equal to GTID_SUBTRACT(@@GLOBAL.gtid_executed, @@GLOBAL.gtid_purged); that is, to all transactions in the binary log that have not yet been purged.

    Issuing RESET MASTER causes the global value (but not the session value) of this variable to be reset to an empty string. GTIDs are not otherwise removed from this set other than when the set is cleared due to RESET MASTER.

    In some older releases, this variable could also be used with session scope, where it contained a representation of the set of transactions that are written to the cache in the current session. The session scope is now deprecated.

  • gtid_executed_compression_period

    Command-Line Format --gtid-executed-compression-period=#
    System Variable gtid_executed_compression_period
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Integer
    Default Value (鈮?8.0.23) 0
    Default Value (鈮?8.0.22) 1000
    Minimum Value 0
    Maximum Value 4294967295

    Compress the mysql.gtid_executed table each time this many transactions have been processed. When binary logging is enabled on the server, this compression method is not used, and instead the mysql.gtid_executed table is compressed on each binary log rotation. When binary logging is disabled on the server, the compression thread sleeps until the specified number of transactions have been executed, then wakes up to perform compression of the mysql.gtid_executed table. Setting the value of this system variable to 0 means that the thread never wakes up, so this explicit compression method is not used. Instead, compression occurs implicitly as required.

    From MySQL 8.0.17, InnoDB transactions are written to the mysql.gtid_executed table by a separate process to non-InnoDB transactions. If the server has a mix of InnoDB transactions and non-InnoDB transactions, the compression controlled by this system variable interferes with the work of this process and can slow it significantly. For this reason, from that release it is recommended that you set gtid_executed_compression_period to 0.

    From MySQL 8.0.23, InnoDB and non-InnoDB transactions are written to the mysql.gtid_executed table by the same process, and the gtid_executed_compression_period default value is 0.

    See mysql.gtid_executed Table Compression for more information.

  • gtid_mode

    Command-Line Format --gtid-mode=MODE
    System Variable gtid_mode
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Enumeration
    Default Value OFF
    Valid Values

    OFF

    OFF_PERMISSIVE

    ON_PERMISSIVE

    ON

    Controls whether GTID based logging is enabled and what type of transactions the logs can contain. You must have privileges sufficient to set global system variables. See Section 5.1.9.1, 鈥淪ystem Variable Privileges鈥?/a>. enforce_gtid_consistency must be set to ON before you can set gtid_mode=ON. Before modifying this variable, see Section 17.1.4, 鈥淐hanging GTID Mode on Online Servers鈥?/a>.

    Logged transactions can be either anonymous or use GTIDs. Anonymous transactions rely on binary log file and position to identify specific transactions. GTID transactions have a unique identifier that is used to refer to transactions. The different modes are:

    • OFF: Both new and replicated transactions must be anonymous.

    • OFF_PERMISSIVE: New transactions are anonymous. Replicated transactions can be either anonymous or GTID transactions.

    • ON_PERMISSIVE: New transactions are GTID transactions. Replicated transactions can be either anonymous or GTID transactions.

    • ON: Both new and replicated transactions must be GTID transactions.

    Changes from one value to another can only be one step at a time. For example, if gtid_mode is currently set to OFF_PERMISSIVE, it is possible to change to OFF or ON_PERMISSIVE but not to ON.

    The values of gtid_purged and gtid_executed are persistent regardless of the value of gtid_mode. Therefore even after changing the value of gtid_mode, these variables contain the correct values.

  • gtid_next

    System Variable gtid_next
    Scope Session
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Enumeration
    Default Value AUTOMATIC
    Valid Values

    AUTOMATIC

    ANONYMOUS

    UUID:NUMBER

    This variable is used to specify whether and how the next GTID is obtained.

    Setting the session value of this system variable is a restricted operation. The session user must have either the REPLICATION_APPLIER privilege (see Section 17.3.3, 鈥淩eplication Privilege Checks鈥?/a>), or privileges sufficient to set restricted session variables (see Section 5.1.9.1, 鈥淪ystem Variable Privileges鈥?/a>).

    gtid_next can take any of the following values:

    • AUTOMATIC: Use the next automatically-generated global transaction ID.

    • ANONYMOUS: Transactions do not have global identifiers, and are identified by file and position only.

    • A global transaction ID in UUID:NUMBER format.

    Exactly which of the above options are valid depends on the setting of gtid_mode, see Section 17.1.4.1, 鈥淩eplication Mode Concepts鈥?/a> for more information. Setting this variable has no effect if gtid_mode is OFF.

    After this variable has been set to UUID:NUMBER, and a transaction has been committed or rolled back, an explicit SET GTID_NEXT statement must again be issued before any other statement.

    DROP TABLE or DROP TEMPORARY TABLE fails with an explicit error when used on a combination of nontemporary tables with temporary tables, or of temporary tables using transactional storage engines with temporary tables using nontransactional storage engines.

  • gtid_owned

    System Variable gtid_owned
    Scope Global, Session
    Dynamic No
    SET_VAR Hint Applies No
    Type String
    Unit set of GTIDs

    This read-only variable is primarily for internal use. Its contents depend on its scope.

    • When used with global scope, gtid_owned holds a list of all the GTIDs that are currently in use on the server, with the IDs of the threads that own them. This variable is mainly useful for a multi-threaded replica to check whether a transaction is already being applied on another thread. An applier thread takes ownership of a transaction's GTID all the time it is processing the transaction, so @@global.gtid_owned shows the GTID and owner for the duration of processing. When a transaction has been committed (or rolled back), the applier thread releases ownership of the GTID.

    • When used with session scope, gtid_owned holds a single GTID that is currently in use by and owned by this session. This variable is mainly useful for testing and debugging the use of GTIDs when the client has explicitly assigned a GTID for the transaction by setting gtid_next. In this case, @@session.gtid_owned displays the GTID all the time the client is processing the transaction, until the transaction has been committed (or rolled back). When the client has finished processing the transaction, the variable is cleared. If gtid_next=AUTOMATIC is used for the session, gtid_owned is populated only briefly during the execution of the commit statement for the transaction, so it cannot be observed from the session concerned, although it is listed if @@global.gtid_owned is read at the right point. If you have a requirement to track the GTIDs that are handled by a client in a session, you can enable the session state tracker controlled by the session_track_gtids system variable.

  • gtid_purged

    System Variable gtid_purged
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type String
    Unit set of GTIDs

    The global value of the gtid_purged system variable (@@GLOBAL.gtid_purged) is a GTID set consisting of the GTIDs of all the transactions that have been committed on the server, but do not exist in any binary log file on the server. gtid_purged is a subset of gtid_executed. The following categories of GTIDs are in gtid_purged:

    • GTIDs of replicated transactions that were committed with binary logging disabled on the replica.

    • GTIDs of transactions that were written to a binary log file that has now been purged.

    • GTIDs that were added explicitly to the set by the statement SET @@GLOBAL.gtid_purged.

    When the server starts, the global value of gtid_purged is initialized to a set of GTIDs. For information on how this GTID set is computed, see The gtid_purged System Variable. If binary logs from MySQL 5.7.7 or older are present on the server, you might need to set binlog_gtid_simple_recovery=FALSE in the server's configuration file to produce the correct computation. See the description for binlog_gtid_simple_recovery for details of the situations in which this setting is needed.

    Issuing RESET MASTER causes the value of gtid_purged to be reset to an empty string.

    You can set the value of gtid_purged in order to record on the server that the transactions in a certain GTID set have been applied, although they do not exist in any binary log on the server. An example use case for this action is when you are restoring a backup of one or more databases on a server, but you do not have the relevant binary logs containing the transactions on the server.

    Important

    GTIDs are only available on a server instance up to the number of non-negative values for a signed 64-bit integer (2 to the power of 63, minus 1). If you set the value of gtid_purged to a number that approaches this limit, subsequent commits can cause the server to run out of GTIDs and take the action specified by binlog_error_action. From MySQL 8.0.23, a warning message is issued when the server instance is approaching the limit.

    From MySQL 8.0, there are two ways to set the value of gtid_purged. You can either replace the value of gtid_purged with your specified GTID set, or you can append your specified GTID set to the GTID set that is already held by gtid_purged. If the server has no existing GTIDs, for example an empty server that you are provisioning with a backup of an existing database, both methods have the same result. If you are restoring a backup that overlaps the transactions that are already on the server, for example replacing a corrupted table with a partial dump from the source made using mysqldump (which includes the GTIDs of all the transactions on the server, even though the dump is partial), use the first method of replacing the value of gtid_purged. If you are restoring a backup that is disjoint from the transactions that are already on the server, for example provisioning a multi-source replica using dumps from two different servers, use the second method of adding to the value of gtid_purged.

    • To replace the value of gtid_purged with your specified GTID set, use the following statement:

      Press CTRL+C to copy
      SET @@GLOBAL.gtid_purged = 'gtid_set'

      gtid_set must be a superset of the current value of gtid_purged, and must not intersect with gtid_subtract(gtid_executed,gtid_purged). In other words, the new GTID set must include any GTIDs that were already in gtid_purged, and must not include any GTIDs in gtid_executed that have not yet been purged. gtid_set also cannot include any GTIDs that are in @@global.gtid_owned, that is, the GTIDs for transactions that are currently being processed on the server.

      The result is that the global value of gtid_purged is set equal to gtid_set, and the value of gtid_executed becomes the union of gtid_set and the previous value of gtid_executed.

    • To append your specified GTID set to gtid_purged, use the following statement with a plus sign (+) before the GTID set:

      Press CTRL+C to copy
      SET @@GLOBAL.gtid_purged = '+gtid_set'

      gtid_set must not intersect with the current value of gtid_executed. In other words, the new GTID set must not include any GTIDs in gtid_executed, including transactions that are already also in gtid_purged. gtid_set also cannot include any GTIDs that are in @@global.gtid_owned, that is, the GTIDs for transactions that are currently being processed on the server.

      The result is that gtid_set is added to both gtid_executed and gtid_purged.

Note

If any binary logs from MySQL 5.7.7 or older are present on the server (for example, following an upgrade of an older server to MySQL 8.0), after issuing a SET @@GLOBAL.gtid_purged statement, you might need to set binlog_gtid_simple_recovery=FALSE in the server's configuration file before restarting the server, otherwise gtid_purged can be computed incorrectly. See the description for binlog_gtid_simple_recovery for details of the situations in which this setting is needed.


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MySQL 8.0 Reference Manual  /  The InnoDB Storage Engine  /  InnoDB Startup Options and System Variables

15.14 InnoDB Startup Options and System Variables

Table 15.24 InnoDB Option and Variable Reference

Name Cmd-Line Option File System Var Status Var Var Scope Dynamic
daemon_memcached_enable_binlog Yes Yes Yes Global No
daemon_memcached_engine_lib_name Yes Yes Yes Global No
daemon_memcached_engine_lib_path Yes Yes Yes Global No
daemon_memcached_option Yes Yes Yes Global No
daemon_memcached_r_batch_size Yes Yes Yes Global No
daemon_memcached_w_batch_size Yes Yes Yes Global No
foreign_key_checks Yes Both Yes
innodb Yes Yes
innodb_adaptive_flushing Yes Yes Yes Global Yes
innodb_adaptive_flushing_lwm Yes Yes Yes Global Yes
innodb_adaptive_hash_index Yes Yes Yes Global Yes
innodb_adaptive_hash_index_parts Yes Yes Yes Global No
innodb_adaptive_max_sleep_delay Yes Yes Yes Global Yes
innodb_api_bk_commit_interval Yes Yes Yes Global Yes
innodb_api_disable_rowlock Yes Yes Yes Global No
innodb_api_enable_binlog Yes Yes Yes Global No
innodb_api_enable_mdl Yes Yes Yes Global No
innodb_api_trx_level Yes Yes Yes Global Yes
innodb_autoextend_increment Yes Yes Yes Global Yes
innodb_autoinc_lock_mode Yes Yes Yes Global No
innodb_background_drop_list_empty Yes Yes Yes Global Yes
Innodb_buffer_pool_bytes_data Yes Global No
Innodb_buffer_pool_bytes_dirty Yes Global No
innodb_buffer_pool_chunk_size Yes Yes Yes Global No
innodb_buffer_pool_debug Yes Yes Yes Global No
innodb_buffer_pool_dump_at_shutdown Yes Yes Yes Global Yes
innodb_buffer_pool_dump_now Yes Yes Yes Global Yes
innodb_buffer_pool_dump_pct Yes Yes Yes Global Yes
Innodb_buffer_pool_dump_status Yes Global No
innodb_buffer_pool_filename Yes Yes Yes Global Yes
innodb_buffer_pool_in_core_file Yes Yes Yes Global Yes
innodb_buffer_pool_instances Yes Yes Yes Global No
innodb_buffer_pool_load_abort Yes Yes Yes Global Yes
innodb_buffer_pool_load_at_startup Yes Yes Yes Global No
innodb_buffer_pool_load_now Yes Yes Yes Global Yes
Innodb_buffer_pool_load_status Yes Global No
Innodb_buffer_pool_pages_data Yes Global No
Innodb_buffer_pool_pages_dirty Yes Global No
Innodb_buffer_pool_pages_flushed Yes Global No
Innodb_buffer_pool_pages_free Yes Global No
Innodb_buffer_pool_pages_latched Yes Global No
Innodb_buffer_pool_pages_misc Yes Global No
Innodb_buffer_pool_pages_total Yes Global No
Innodb_buffer_pool_read_ahead Yes Global No
Innodb_buffer_pool_read_ahead_evicted Yes Global No
Innodb_buffer_pool_read_ahead_rnd Yes Global No
Innodb_buffer_pool_read_requests Yes Global No
Innodb_buffer_pool_reads Yes Global No
Innodb_buffer_pool_resize_status Yes Global No
innodb_buffer_pool_size Yes Yes Yes Global Yes
Innodb_buffer_pool_wait_free Yes Global No
Innodb_buffer_pool_write_requests Yes Global No
innodb_change_buffer_max_size Yes Yes Yes Global Yes
innodb_change_buffering Yes Yes Yes Global Yes
innodb_change_buffering_debug Yes Yes Yes Global Yes
innodb_checkpoint_disabled Yes Yes Yes Global Yes
innodb_checksum_algorithm Yes Yes Yes Global Yes
innodb_cmp_per_index_enabled Yes Yes Yes Global Yes
innodb_commit_concurrency Yes Yes Yes Global Yes
innodb_compress_debug Yes Yes Yes Global Yes
innodb_compression_failure_threshold_pct Yes Yes Yes Global Yes
innodb_compression_level Yes Yes Yes Global Yes
innodb_compression_pad_pct_max Yes Yes Yes Global Yes
innodb_concurrency_tickets Yes Yes Yes Global Yes
innodb_data_file_path Yes Yes Yes Global No
Innodb_data_fsyncs Yes Global No
innodb_data_home_dir Yes Yes Yes Global No
Innodb_data_pending_fsyncs Yes Global No
Innodb_data_pending_reads Yes Global No
Innodb_data_pending_writes Yes Global No
Innodb_data_read Yes Global No
Innodb_data_reads Yes Global No
Innodb_data_writes Yes Global No
Innodb_data_written Yes Global No
Innodb_dblwr_pages_written Yes Global No
Innodb_dblwr_writes Yes Global No
innodb_ddl_buffer_size Yes Yes Yes Both Yes
innodb_ddl_log_crash_reset_debug Yes Yes Yes Global Yes
innodb_ddl_threads Yes Yes Yes Both Yes
innodb_deadlock_detect Yes Yes Yes Global Yes
innodb_dedicated_server Yes Yes Yes Global No
innodb_default_row_format Yes Yes Yes Global Yes
innodb_directories Yes Yes Yes Global No
innodb_disable_sort_file_cache Yes Yes Yes Global Yes
innodb_doublewrite Yes Yes Yes Global Varies
innodb_doublewrite_batch_size Yes Yes Yes Global No
innodb_doublewrite_dir Yes Yes Yes Global No
innodb_doublewrite_files Yes Yes Yes Global No
innodb_doublewrite_pages Yes Yes Yes Global No
innodb_fast_shutdown Yes Yes Yes Global Yes
innodb_fil_make_page_dirty_debug Yes Yes Yes Global Yes
innodb_file_per_table Yes Yes Yes Global Yes
innodb_fill_factor Yes Yes Yes Global Yes
innodb_flush_log_at_timeout Yes Yes Yes Global Yes
innodb_flush_log_at_trx_commit Yes Yes Yes Global Yes
innodb_flush_method Yes Yes Yes Global No
innodb_flush_neighbors Yes Yes Yes Global Yes
innodb_flush_sync Yes Yes Yes Global Yes
innodb_flushing_avg_loops Yes Yes Yes Global Yes
innodb_force_load_corrupted Yes Yes Yes Global No
innodb_force_recovery Yes Yes Yes Global No
innodb_fsync_threshold Yes Yes Yes Global Yes
innodb_ft_aux_table Yes Global Yes
innodb_ft_cache_size Yes Yes Yes Global No
innodb_ft_enable_diag_print Yes Yes Yes Global Yes
innodb_ft_enable_stopword Yes Yes Yes Both Yes
innodb_ft_max_token_size Yes Yes Yes Global No
innodb_ft_min_token_size Yes Yes Yes Global No
innodb_ft_num_word_optimize Yes Yes Yes Global Yes
innodb_ft_result_cache_limit Yes Yes Yes Global Yes
innodb_ft_server_stopword_table Yes Yes Yes Global Yes
innodb_ft_sort_pll_degree Yes Yes Yes Global No
innodb_ft_total_cache_size Yes Yes Yes Global No
innodb_ft_user_stopword_table Yes Yes Yes Both Yes
Innodb_have_atomic_builtins Yes Global No
innodb_idle_flush_pct Yes Yes Yes Global Yes
innodb_io_capacity Yes Yes Yes Global Yes
innodb_io_capacity_max Yes Yes Yes Global Yes
innodb_limit_optimistic_insert_debug Yes Yes Yes Global Yes
innodb_lock_wait_timeout Yes Yes Yes Both Yes
innodb_log_buffer_size Yes Yes Yes Global Varies
innodb_log_checkpoint_fuzzy_now Yes Yes Yes Global Yes
innodb_log_checkpoint_now Yes Yes Yes Global Yes
innodb_log_checksums Yes Yes Yes Global Yes
innodb_log_compressed_pages Yes Yes Yes Global Yes
innodb_log_file_size Yes Yes Yes Global No
innodb_log_files_in_group Yes Yes Yes Global No
innodb_log_group_home_dir Yes Yes Yes Global No
innodb_log_spin_cpu_abs_lwm Yes Yes Yes Global Yes
innodb_log_spin_cpu_pct_hwm Yes Yes Yes Global Yes
innodb_log_wait_for_flush_spin_hwm Yes Yes Yes Global Yes
Innodb_log_waits Yes Global No
innodb_log_write_ahead_size Yes Yes Yes Global Yes
Innodb_log_write_requests Yes Global No
innodb_log_writer_threads Yes Yes Yes Global Yes
Innodb_log_writes Yes Global No
innodb_lru_scan_depth Yes Yes Yes Global Yes
innodb_max_dirty_pages_pct Yes Yes Yes Global Yes
innodb_max_dirty_pages_pct_lwm Yes Yes Yes Global Yes
innodb_max_purge_lag Yes Yes Yes Global Yes
innodb_max_purge_lag_delay Yes Yes Yes Global Yes
innodb_max_undo_log_size Yes Yes Yes Global Yes
innodb_merge_threshold_set_all_debug Yes Yes Yes Global Yes
innodb_monitor_disable Yes Yes Yes Global Yes
innodb_monitor_enable Yes Yes Yes Global Yes
innodb_monitor_reset Yes Yes Yes Global Yes
innodb_monitor_reset_all Yes Yes Yes Global Yes
Innodb_num_open_files Yes Global No
innodb_numa_interleave Yes Yes Yes Global No
innodb_old_blocks_pct Yes Yes Yes Global Yes
innodb_old_blocks_time Yes Yes Yes Global Yes
innodb_online_alter_log_max_size Yes Yes Yes Global Yes
innodb_open_files Yes Yes Yes Global Varies
innodb_optimize_fulltext_only Yes Yes Yes Global Yes
Innodb_os_log_fsyncs Yes Global No
Innodb_os_log_pending_fsyncs Yes Global No
Innodb_os_log_pending_writes Yes Global No
Innodb_os_log_written Yes Global No
innodb_page_cleaners Yes Yes Yes Global No
Innodb_page_size Yes Global No
innodb_page_size Yes Yes Yes Global No
Innodb_pages_created Yes Global No
Innodb_pages_read Yes Global No
Innodb_pages_written Yes Global No
innodb_parallel_read_threads Yes Yes Yes Session Yes
innodb_print_all_deadlocks Yes Yes Yes Global Yes
innodb_print_ddl_logs Yes Yes Yes Global Yes
innodb_purge_batch_size Yes Yes Yes Global Yes
innodb_purge_rseg_truncate_frequency Yes Yes Yes Global Yes
innodb_purge_threads Yes Yes Yes Global No
innodb_random_read_ahead Yes Yes Yes Global Yes
innodb_read_ahead_threshold Yes Yes Yes Global Yes
innodb_read_io_threads Yes Yes Yes Global No
innodb_read_only Yes Yes Yes Global No
innodb_redo_log_archive_dirs Yes Yes Yes Global Yes
innodb_redo_log_capacity Yes Yes Yes Global Yes
Innodb_redo_log_capacity_resized Yes Global No
Innodb_redo_log_checkpoint_lsn Yes Global No
Innodb_redo_log_current_lsn Yes Global No
Innodb_redo_log_enabled Yes Global No
innodb_redo_log_encrypt Yes Yes Yes Global Yes
Innodb_redo_log_flushed_to_disk_lsn Yes Global No
Innodb_redo_log_logical_size Yes Global No
Innodb_redo_log_physical_size Yes Global No
Innodb_redo_log_read_only Yes Global No
Innodb_redo_log_resize_status Yes Global No
Innodb_redo_log_uuid Yes Global No
innodb_replication_delay Yes Yes Yes Global Yes
innodb_rollback_on_timeout Yes Yes Yes Global No
innodb_rollback_segments Yes Yes Yes Global Yes
Innodb_row_lock_current_waits Yes Global No
Innodb_row_lock_time Yes Global No
Innodb_row_lock_time_avg Yes Global No
Innodb_row_lock_time_max Yes Global No
Innodb_row_lock_waits Yes Global No
Innodb_rows_deleted Yes Global No
Innodb_rows_inserted Yes Global No
Innodb_rows_read Yes Global No
Innodb_rows_updated Yes Global No
innodb_saved_page_number_debug Yes Yes Yes Global Yes
innodb_segment_reserve_factor Yes Yes Yes Global Yes
innodb_sort_buffer_size Yes Yes Yes Global No
innodb_spin_wait_delay Yes Yes Yes Global Yes
innodb_spin_wait_pause_multiplier Yes Yes Yes Global Yes
innodb_stats_auto_recalc Yes Yes Yes Global Yes
innodb_stats_include_delete_marked Yes Yes Yes Global Yes
innodb_stats_method Yes Yes Yes Global Yes
innodb_stats_on_metadata Yes Yes Yes Global Yes
innodb_stats_persistent Yes Yes Yes Global Yes
innodb_stats_persistent_sample_pages Yes Yes Yes Global Yes
innodb_stats_transient_sample_pages Yes Yes Yes Global Yes
innodb-status-file Yes Yes
innodb_status_output Yes Yes Yes Global Yes
innodb_status_output_locks Yes Yes Yes Global Yes
innodb_strict_mode Yes Yes Yes Both Yes
innodb_sync_array_size Yes Yes Yes Global No
innodb_sync_debug Yes Yes Yes Global No
innodb_sync_spin_loops Yes Yes Yes Global Yes
Innodb_system_rows_deleted Yes Global No
Innodb_system_rows_inserted Yes Global No
Innodb_system_rows_read Yes Global No
innodb_table_locks Yes Yes Yes Both Yes
innodb_temp_data_file_path Yes Yes Yes Global No
innodb_temp_tablespaces_dir Yes Yes Yes Global No
innodb_thread_concurrency Yes Yes Yes Global Yes
innodb_thread_sleep_delay Yes Yes Yes Global Yes
innodb_tmpdir Yes Yes Yes Both Yes
Innodb_truncated_status_writes Yes Global No
innodb_trx_purge_view_update_only_debug Yes Yes Yes Global Yes
innodb_trx_rseg_n_slots_debug Yes Yes Yes Global Yes
innodb_undo_directory Yes Yes Yes Global No
innodb_undo_log_encrypt Yes Yes Yes Global Yes
innodb_undo_log_truncate Yes Yes Yes Global Yes
innodb_undo_tablespaces Yes Yes Yes Global Varies
Innodb_undo_tablespaces_active Yes Global No
Innodb_undo_tablespaces_explicit Yes Global No
Innodb_undo_tablespaces_implicit Yes Global No
Innodb_undo_tablespaces_total Yes Global No
innodb_use_fdatasync Yes Yes Yes Global Yes
innodb_use_native_aio Yes Yes Yes Global No
innodb_validate_tablespace_paths Yes Yes Yes Global No
innodb_version Yes Global No
innodb_write_io_threads Yes Yes Yes Global No
unique_checks Yes Both Yes
Name Cmd-Line Option File System Var Status Var Var Scope Dynamic

InnoDB Command Options

  • --innodb[=value]

    Command-Line Format --innodb[=value]
    Deprecated Yes
    Type Enumeration
    Default Value ON
    Valid Values

    OFF

    ON

    FORCE

    Controls loading of the InnoDB storage engine, if the server was compiled with InnoDB support. This option has a tristate format, with possible values of OFF, ON, or FORCE. See Section 5.6.1, 鈥淚nstalling and Uninstalling Plugins鈥?/a>.

    To disable InnoDB, use --innodb=OFF or --skip-innodb. In this case, because the default storage engine is InnoDB, the server does not start unless you also use --default-storage-engine and --default-tmp-storage-engine to set the default to some other engine for both permanent and TEMPORARY tables.

    The InnoDB storage engine can no longer be disabled, and the --innodb=OFF and --skip-innodb options are deprecated and have no effect. Their use results in a warning. Expect these options to be removed in a future MySQL release.

  • --innodb-status-file

    Command-Line Format --innodb-status-file[={OFF|ON}]
    Type Boolean
    Default Value OFF

    The --innodb-status-file startup option controls whether InnoDB creates a file named innodb_status.pid in the data directory and writes SHOW ENGINE INNODB STATUS output to it every 15 seconds, approximately.

    The innodb_status.pid file is not created by default. To create it, start mysqld with the --innodb-status-file option. InnoDB removes the file when the server is shut down normally. If an abnormal shutdown occurs, the status file may have to be removed manually.

    The --innodb-status-file option is intended for temporary use, as SHOW ENGINE INNODB STATUS output generation can affect performance, and the innodb_status.pid file can become quite large over time.

    For related information, see Section 15.17.2, 鈥淓nabling InnoDB Monitors鈥?/a>.

  • --skip-innodb

    Disable the InnoDB storage engine. See the description of --innodb.

InnoDB System Variables


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MySQL 8.0 Reference Manual  /  ...  /  MySQL Server Options and Variables for NDB Cluster

23.4.3.9 MySQL Server Options and Variables for NDB Cluster

This section provides information about MySQL server options, server and status variables that are specific to NDB Cluster. For general information on using these, and for other options and variables not specific to NDB Cluster, see Section 5.1, 鈥淭he MySQL Server鈥?/a>.

For NDB Cluster configuration parameters used in the cluster configuration file (usually named config.ini), see Section 23.4, 鈥淐onfiguration of NDB Cluster鈥?/a>.

23.4.3.9.1 MySQL Server Options for NDB Cluster

This section provides descriptions of mysqld server options relating to NDB Cluster. For information about mysqld options not specific to NDB Cluster, and for general information about the use of options with mysqld, see Section 5.1.7, 鈥淪erver Command Options鈥?/a>.

For information about command-line options used with other NDB Cluster processes, see Section 23.5, 鈥淣DB Cluster Programs鈥?/a>.

  • --ndbcluster

    Command-Line Format --ndbcluster[=value]
    Disabled by skip-ndbcluster
    Type Enumeration
    Default Value ON
    Valid Values

    OFF

    FORCE

    The NDBCLUSTER storage engine is necessary for using NDB Cluster. If a mysqld binary includes support for the NDBCLUSTER storage engine, the engine is disabled by default. Use the --ndbcluster option to enable it. Use --skip-ndbcluster to explicitly disable the engine.

    The --ndbcluster option is ignored (and the NDB storage engine is not enabled) if --initialize is also used. (It is neither necessary nor desirable to use this option together with --initialize.)

  • --ndb-allow-copying-alter-table=[ON|OFF]

    Command-Line Format --ndb-allow-copying-alter-table[={OFF|ON}]
    System Variable ndb_allow_copying_alter_table
    Scope Global, Session
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Boolean
    Default Value ON

    Let ALTER TABLE and other DDL statements use copying operations on NDB tables. Set to OFF to keep this from happening; doing so may improve performance of critical applications.

  • --ndb-applier-allow-skip-epoch

    Command-Line Format --ndb-applier-allow-skip-epoch
    Introduced 8.0.28-ndb-8.0.28
    System Variable ndb_applier_allow_skip_epoch
    Scope Global
    Dynamic No
    SET_VAR Hint Applies No

    Use together with --slave-skip-errors to cause NDB to ignore skipped epoch transactions. Has no effect when used alone.

  • --ndb-batch-size=#

    Command-Line Format --ndb-batch-size
    System Variable ndb_batch_size
    Scope Global
    Dynamic No
    SET_VAR Hint Applies No
    Type Integer
    Default Value 32768
    Minimum Value 0
    Maximum Value (鈮?8.0.29-ndb-8.0.29) 2147483648
    Maximum Value 2147483648
    Maximum Value 2147483648
    Maximum Value (鈮?8.0.28-ndb-8.0.28) 31536000
    Unit bytes

    This sets the size in bytes that is used for NDB transaction batches.

  • --ndb-cluster-connection-pool=#

    Command-Line Format --ndb-cluster-connection-pool
    System Variable ndb_cluster_connection_pool
    System Variable ndb_cluster_connection_pool
    Scope Global
    Scope Global
    Dynamic No
    Dynamic No
    SET_VAR Hint Applies No
    SET_VAR Hint Applies No
    Type Integer
    Default Value 1
    Minimum Value 1
    Maximum Value 63

    By setting this option to a value greater than 1 (the default), a mysqld process can use multiple connections to the cluster, effectively mimicking several SQL nodes. Each connection requires its own [api] or [mysqld] section in the cluster configuration (config.ini) file, and counts against the maximum number of API connections supported by the cluster.

    Suppose that you have 2 cluster host computers, each running an SQL node whose mysqld process was started with --ndb-cluster-connection-pool=4; this means that the cluster must have 8 API slots available for these connections (instead of 2). All of these connections are set up when the SQL node connects to the cluster, and are allocated to threads in a round-robin fashion.

    This option is useful only when running mysqld on host machines having multiple CPUs, multiple cores, or both. For best results, the value should be smaller than the total number of cores available on the host machine. Setting it to a value greater than this is likely to degrade performance severely.

    Important

    Because each SQL node using connection pooling occupies multiple API node slots鈥攅ach slot having its own node ID in the cluster鈥攜ou must not use a node ID as part of the cluster connection string when starting any mysqld process that employs connection pooling.

    Setting a node ID in the connection string when using the --ndb-cluster-connection-pool option causes node ID allocation errors when the SQL node attempts to connect to the cluster.

  • --ndb-cluster-connection-pool-nodeids=list

    Command-Line Format --ndb-cluster-connection-pool-nodeids
    System Variable ndb_cluster_connection_pool_nodeids
    Scope Global
    Dynamic No
    SET_VAR Hint Applies No
    Type Set
    Default Value

    Specifies a comma-separated list of node IDs for connections to the cluster used by an SQL node. The number of nodes in this list must be the same as the value set for the --ndb-cluster-connection-pool option.

  • --ndb-blob-read-batch-bytes=bytes

    Command-Line Format --ndb-blob-read-batch-bytes
    System Variable ndb_blob_read_batch_bytes
    Scope Global, Session
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Integer
    Default Value 65536
    Minimum Value 0
    Maximum Value 4294967295

    This option can be used to set the size (in bytes) for batching of BLOB data reads in NDB Cluster applications. When this batch size is exceeded by the amount of BLOB data to be read within the current transaction, any pending BLOB read operations are immediately executed.

    The maximum value for this option is 4294967295; the default is 65536. Setting it to 0 has the effect of disabling BLOB read batching.

    Note

    In NDB API applications, you can control BLOB write batching with the setMaxPendingBlobReadBytes() and getMaxPendingBlobReadBytes() methods.

  • --ndb-blob-write-batch-bytes=bytes

    Command-Line Format --ndb-blob-write-batch-bytes
    System Variable ndb_blob_write_batch_bytes
    Scope Global, Session
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Integer
    Default Value 65536
    Minimum Value 0
    Maximum Value 4294967295
    Unit bytes

    This option can be used to set the size (in bytes) for batching of BLOB data writes in NDB Cluster applications. When this batch size is exceeded by the amount of BLOB data to be written within the current transaction, any pending BLOB write operations are immediately executed.

    The maximum value for this option is 4294967295; the default is 65536. Setting it to 0 has the effect of disabling BLOB write batching.

    Note

    In NDB API applications, you can control BLOB write batching with the setMaxPendingBlobWriteBytes() and getMaxPendingBlobWriteBytes() methods.

  • --ndb-connectstring=connection_string

    Command-Line Format --ndb-connectstring
    Type String

    When using the NDBCLUSTER storage engine, this option specifies the management server that distributes cluster configuration data. See Section 23.4.3.3, 鈥淣DB Cluster Connection Strings鈥?/a>, for syntax.

  • --ndb-default-column-format=[FIXED|DYNAMIC]

    Command-Line Format --ndb-default-column-format={FIXED|DYNAMIC}
    System Variable ndb_default_column_format
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Enumeration
    Default Value FIXED
    Valid Values

    FIXED

    DYNAMIC

    Sets the default COLUMN_FORMAT and ROW_FORMAT for new tables (see Section 13.1.20, 鈥淐REATE TABLE Statement鈥?/a>). The default is FIXED.

  • --ndb-deferred-constraints=[0|1]

    Command-Line Format --ndb-deferred-constraints
    System Variable ndb_deferred_constraints
    Scope Global, Session
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Integer
    Default Value 0
    Minimum Value 0
    Maximum Value 1

    Controls whether or not constraint checks on unique indexes are deferred until commit time, where such checks are supported. 0 is the default.

    This option is not normally needed for operation of NDB Cluster or NDB Cluster Replication, and is intended primarily for use in testing.

  • --ndb-schema-dist-timeout=#

    Command-Line Format --ndb-schema-dist-timeout=#
    Introduced 8.0.17-ndb-8.0.17
    System Variable ndb_schema_dist_timeout
    Scope Global
    Dynamic No
    SET_VAR Hint Applies No
    Type Integer
    Default Value 120
    Minimum Value 5
    Maximum Value 1200
    Unit seconds

    Specifies the maximum time in seconds that this mysqld waits for a schema operation to complete before marking it as having timed out.

  • --ndb-distribution=[KEYHASH|LINHASH]

    Command-Line Format --ndb-distribution={KEYHASH|LINHASH}
    System Variable ndb_distribution
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Enumeration
    Default Value KEYHASH
    Valid Values

    LINHASH

    KEYHASH

    Controls the default distribution method for NDB tables. Can be set to either of KEYHASH (key hashing) or LINHASH (linear hashing). KEYHASH is the default.

  • --ndb-log-apply-status

    Command-Line Format --ndb-log-apply-status[={OFF|ON}]
    System Variable ndb_log_apply_status
    Scope Global
    Dynamic No
    SET_VAR Hint Applies No
    Type Boolean
    Default Value OFF

    Causes a replica mysqld to log any updates received from its immediate source to the mysql.ndb_apply_status table in its own binary log using its own server ID rather than the server ID of the source. In a circular or chain replication setting, this allows such updates to propagate to the mysql.ndb_apply_status tables of any MySQL servers configured as replicas of the current mysqld.

    In a chain replication setup, using this option allows downstream (replica) clusters to be aware of their positions relative to all of their upstream contributors (sourcess).

    In a circular replication setup, this option causes changes to ndb_apply_status tables to complete the entire circuit, eventually propagating back to the originating NDB Cluster. This also allows a cluster acting as a replication source to see when its changes (epochs) have been applied to the other clusters in the circle.

    This option has no effect unless the MySQL server is started with the --ndbcluster option.

  • --ndb-log-empty-epochs=[ON|OFF]

    Command-Line Format --ndb-log-empty-epochs[={OFF|ON}]
    System Variable ndb_log_empty_epochs
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Boolean
    Default Value OFF

    Causes epochs during which there were no changes to be written to the ndb_apply_status and ndb_binlog_index tables, even when log_replica_updates or log_slave_updates is enabled.

    By default this option is disabled. Disabling --ndb-log-empty-epochs causes epoch transactions with no changes not to be written to the binary log, although a row is still written even for an empty epoch in ndb_binlog_index.

    Because --ndb-log-empty-epochs=1 causes the size of the ndb_binlog_index table to increase independently of the size of the binary log, users should be prepared to manage the growth of this table, even if they expect the cluster to be idle a large part of the time.

  • --ndb-log-empty-update=[ON|OFF]

    Command-Line Format --ndb-log-empty-update[={OFF|ON}]
    System Variable ndb_log_empty_update
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Boolean
    Default Value OFF

    Causes updates that produced no changes to be written to the ndb_apply_status and ndb_binlog_index tables, even when log_replica_updates or log_slave_updates is enabled.

    By default this option is disabled (OFF). Disabling --ndb-log-empty-update causes updates with no changes not to be written to the binary log.

  • --ndb-log-exclusive-reads=[0|1]

    Command-Line Format --ndb-log-exclusive-reads[={OFF|ON}]
    System Variable ndb_log_exclusive_reads
    Scope Global, Session
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Boolean
    Default Value 0

    Starting the server with this option causes primary key reads to be logged with exclusive locks, which allows for NDB Cluster Replication conflict detection and resolution based on read conflicts. You can also enable and disable these locks at runtime by setting the value of the ndb_log_exclusive_reads system variable to 1 or 0, respectively. 0 (disable locking) is the default.

    For more information, see Read conflict detection and resolution.

  • --ndb-log-fail-terminate

    Command-Line Format --ndb-log-fail-terminate
    Introduced 8.0.21-ndb-8.0.21
    System Variable ndb_log_fail_terminate
    Scope Global
    Dynamic No
    SET_VAR Hint Applies No
    Type Boolean
    Default Value FALSE

    When this option is specified, and complete logging of all found row events is not possible, the mysqld process is terminated.

  • --ndb-log-orig

    Command-Line Format --ndb-log-orig[={OFF|ON}]
    System Variable ndb_log_orig
    Scope Global
    Dynamic No
    SET_VAR Hint Applies No
    Type Boolean
    Default Value OFF

    Log the originating server ID and epoch in the ndb_binlog_index table.

    Note

    This makes it possible for a given epoch to have multiple rows in ndb_binlog_index, one for each originating epoch.

    For more information, see Section 23.7.4, 鈥淣DB Cluster Replication Schema and Tables鈥?/a>.

  • --ndb-log-transaction-id

    Command-Line Format --ndb-log-transaction-id[={OFF|ON}]
    System Variable ndb_log_transaction_id
    Scope Global
    Dynamic No
    SET_VAR Hint Applies No
    Type Boolean
    Default Value OFF

    Causes a replica mysqld to write the NDB transaction ID in each row of the binary log. The default value is FALSE.

    --ndb-log-transaction-id is required to enable NDB Cluster Replication conflict detection and resolution using the NDB$EPOCH_TRANS() function (see NDB$EPOCH_TRANS()). For more information, see Section 23.7.11, 鈥淣DB Cluster Replication Conflict Resolution鈥?/a>.

    The deprecated log_bin_use_v1_row_events system variable, which defaults to OFF, must not be set to ON when you use --ndb-log-transaction-id=ON.

  • --ndb-log-update-as-write

    Command-Line Format --ndb-log-update-as-write[={OFF|ON}]
    System Variable ndb_log_update_as_write
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Boolean
    Default Value ON

    Whether updates on the source are written to the binary log as updates (OFF) or writes (ON). When this option is enabled, and both --ndb-log-update-as-write and --ndb-log-update-minimal are disabled, operations of different types are lo堑ged as described in the following list:

    • INSERT: Logged as a WRITE_ROW event with no before image; the after image is logged with all columns.

      UPDATE: Logged as a WRITE_ROW event with no before image; the after image is logged with all columns.

      DELETE: Logged as a DELETE_ROW event with all columns logged in the before image; the after image is not logged.

    This option can be used for NDB Replication conflict resolution in combination with the other two NDB logging options mentioned previously; see ndb_replication Table, for more information.

  • --ndb-log-updated-only

    Command-Line Format --ndb-log-updated-only[={OFF|ON}]
    System Variable ndb_log_updated_only
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Boolean
    Default Value ON

    Whether mysqld writes complete rows (ON) or updates only (OFF) to the binary log. When this option is enabled, and both --ndb-log-update-as-write and --ndb-log-update-minimal are disabled, operations of different types are lo堑ged as described in the following list:

    • INSERT: Logged as a WRITE_ROW event with no before image; the after image is logged with all columns.

    • UPDATE: Logged as an UPDATE_ROW event with primary key columns and updated columns present in both the before and after images.

    • DELETE: Logged as a DELETE_ROW event with primary key columns incuded in the before image; the after image is not logged.

    This option can be used for NDB Replication conflict resolution in combination with the other two NDB logging options mentioned previously; see ndb_replication Table, for more information about how these options interact with one another.

  • --ndb-log-update-minimal

    Command-Line Format --ndb-log-update-minimal[={OFF|ON}]
    System Variable ndb_log_update_minimal
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Boolean
    Default Value OFF

    Log updates in a minimal fashion, by writing only the primary key values in the before image, and only the changed columns in the after image. This may cause compatibility problems if replicating to storage engines other than NDB. When this option is enabled, and both --ndb-log-updated-only and --ndb-log-update-as-write are disabled, operations of different types are lo堑ged as described in the following list:

    • INSERT: Logged as a WRITE_ROW event with no before image; the after image is logged with all columns.

    • UPDATE: Logged as an UPDATE_ROW event with primary key columns in the before image; all columns except primary key columns are logged in the after image.

    • DELETE: Logged as a DELETE_ROW event with all columns in the before image; the after image is not logged.

    This option can be used for NDB Replication conflict resolution in combination with the other two NDB logging options mentioned previously; see ndb_replication Table, for more information.

  • --ndb-mgmd-host=host[:port]

    Command-Line Format --ndb-mgmd-host=host_name[:port_num]
    Type String
    Default Value localhost:1186

    Can be used to set the host and port number of a single management server for the program to connect to. If the program requires node IDs or references to multiple management servers (or both) in its connection information, use the --ndb-connectstring option instead.

  • --ndb-nodeid=#

    Command-Line Format --ndb-nodeid=#
    Status Variable Ndb_cluster_node_id
    Scope Global
    Dynamic No
    Type Integer
    Default Value N/A
    Minimum Value 1
    Maximum Value 255
    Maximum Value 63

    Set this MySQL server's node ID in an NDB Cluster.

    The --ndb-nodeid option overrides any node ID set with --ndb-connectstring, regardless of the order in which the two options are used.

    In addition, if --ndb-nodeid is used, then either a matching node ID must be found in a [mysqld] or [api] section of config.ini, or there must be an 鈥?span class="quote">open鈥?/span> [mysqld] or [api] section in the file (that is, a section without a NodeId or Id parameter specified). This is also true if the node ID is specified as part of the connection string.

    Regardless of how the node ID is determined, its is shown as the value of the global status variable Ndb_cluster_node_id in the output of SHOW STATUS, and as cluster_node_id in the connection row of the output of SHOW ENGINE NDBCLUSTER STATUS.

    For more information about node IDs for NDB Cluster SQL nodes, see Section 23.4.3.7, 鈥淒efining SQL and Other API Nodes in an NDB Cluster鈥?/a>.

  • --ndbinfo={ON|OFF|FORCE}

    Command-Line Format --ndbinfo[=value] (鈮?8.0.13-ndb-8.0.13)
    Introduced 8.0.13-ndb-8.0.13
    Type Enumeration
    Default Value ON
    Valid Values

    ON

    OFF

    FORCE

    Enables the plugin for the ndbinfo information database. By default this is ON whenever NDBCLUSTER is enabled.

  • --ndb-optimization-delay=milliseconds

    Command-Line Format --ndb-optimization-delay=#
    System Variable ndb_optimization_delay
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Integer
    Default Value 10
    Minimum Value 0
    Maximum Value 100000
    Unit milliseconds

    Set the number of milliseconds to wait between sets of rows by OPTIMIZE TABLE statements on NDB tables. The default is 10.

  • --ndb-optimized-node-selection

    Command-Line Format --ndb-optimized-node-selection

    Enable optimizations for selection of nodes for transactions. Enabled by default; use --skip-ndb-optimized-node-selection to disable.

  • --ndb-transid-mysql-connection-map=state

    Command-Line Format --ndb-transid-mysql-connection-map[=state]
    Type Enumeration
    Default Value ON
    Valid Values

    ON

    OFF

    FORCE

    Enables or disables the plugin that handles the ndb_transid_mysql_connection_map table in the INFORMATION_SCHEMA database. Takes one of the values ON, OFF, or FORCE. ON (the default) enables the plugin. OFF disables the plugin, which makes ndb_transid_mysql_connection_map inaccessible. FORCE keeps the MySQL Server from starting if the plugin fails to load and start.

    You can see whether the ndb_transid_mysql_connection_map table plugin is running by checking the output of SHOW PLUGINS.

  • --ndb-wait-connected=seconds

    Command-Line Format --ndb-wait-connected=#
    System Variable ndb_wait_connected
    Scope Global
    Dynamic No
    SET_VAR Hint Applies No
    Type Integer
    Default Value (鈮?8.0.27-ndb-8.0.27) 120
    Default Value (鈮?8.0.26-ndb-8.0.26) 30
    Default Value 30
    Minimum Value 0
    Maximum Value 31536000
    Unit seconds

    This option sets the period of time that the MySQL server waits for connections to NDB Cluster management and data nodes to be established before accepting MySQL client connections. The time is specified in seconds. The default value is 30.

  • --ndb-wait-setup=seconds

    Command-Line Format --ndb-wait-setup=#
    System Variable ndb_wait_setup
    Scope Global
    Dynamic No
    SET_VAR Hint Applies No
    Type Integer
    Default Value (鈮?8.0.27-ndb-8.0.27) 120
    Default Value (鈮?8.0.26-ndb-8.0.26) 30
    Default Value 30
    Default Value 15
    Default Value 15
    Minimum Value 0
    Maximum Value 31536000
    Unit seconds

    This variable shows the period of time that the MySQL server waits for the NDB storage engine to complete setup before timing out and treating NDB as unavailable. The time is specified in seconds. The default value is 30.

  • --skip-ndbcluster

    Command-Line Format --skip-ndbcluster

    Disable the NDBCLUSTER storage engine. This is the default for binaries that were built with NDBCLUSTER storage engine support; the server allocates memory and other resources for this storage engine only if the --ndbcluster option is given explicitly. See Section 23.4.1, 鈥淨uick Test Setup of NDB Cluster鈥?/a>, for an example.

23.4.3.9.2 NDB Cluster System Variables

This section provides detailed information about MySQL server system variables that are specific to NDB Cluster and the NDB storage engine. For system variables not specific to NDB Cluster, see Section 5.1.8, 鈥淪erver System Variables鈥?/a>. For general information on using system variables, see Section 5.1.9, 鈥淯sing System Variables鈥?/a>.

  • ndb_autoincrement_prefetch_sz

    Command-Line Format --ndb-autoincrement-prefetch-sz=#
    System Variable ndb_autoincrement_prefetch_sz
    Scope Global, Session
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Integer
    Default Value (鈮?8.0.19-ndb-8.0.19) 512
    Default Value (鈮?8.0.18-ndb-8.0.18) 1
    Minimum Value 1
    Maximum Value 65536

    Determines the probability of gaps in an autoincremented column. Set it to 1 to minimize this. Setting it to a high value for optimization makes inserts faster, but decreases the likelihood of consecutive autoincrement numbers being used in a batch of inserts.

    This variable affects only the number of AUTO_INCREMENT IDs that are fetched between statements; within a given statement, at least 32 IDs are obtained at a time.

    Important

    This variable does not affect inserts performed using INSERT ... SELECT.

  • ndb_cache_check_time

    Command-Line Format --ndb-cache-check-time=#
    Deprecated Yes
    System Variable ndb_cache_check_time
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Integer
    Default Value 0
    Minimum Value 0
    Maximum Value 31536000
    Unit milliseconds

    The number of milliseconds that elapse between checks of NDB Cluster SQL nodes by the MySQL query cache. Setting this to 0 (the default and minimum value) means that the query cache checks for validation on every query.

    The recommended maximum value for this variable is 1000, which means that the check is performed once per second. A larger value means that the check is performed and possibly invalidated due to updates on different SQL nodes less often. It is generally not desirable to set this to a value greater than 2000.

    Note

    The query cache ndb_cache_check_time are deprecated in MySQL 5.7; the query cache was removed in MySQL 8.0.

  • ndb_clear_apply_status

    Command-Line Format --ndb-clear-apply-status[={OFF|ON}]
    System Variable ndb_clear_apply_status
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Boolean
    Default Value ON

    By the default, executing RESET SLAVE causes an NDB Cluster replica to purge all rows from its ndb_apply_status table. You can disable this by setting ndb_clear_apply_status=OFF.

  • ndb_conflict_role

    Command-Line Format --ndb-conflict-role=value
    Introduced 8.0.23-ndb-8.0.23
    System Variable ndb_conflict_role
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Enumeration
    Default Value NONE
    Valid Values

    NONE

    PRIMARY

    SECONDARY

    PASS

    Determines the role of this SQL node (and NDB Cluster) in a circular (鈥?span class="quote">active-active鈥?/span>) replication setup. ndb_slave_conflict_role can take any one of the values PRIMARY, SECONDARY, PASS, or NULL (the default). The replica SQL thread must be stopped before you can change ndb_slave_conflict_role. In addition, it is not possible to change directly between PASS and either of PRIMARY or SECONDARY directly; in such cases, you must ensure that the SQL thread is stopped, then execute SET @@GLOBAL.ndb_slave_conflict_role = 'NONE' first.

    This variable replaces ndb_slave_conflict_role, which is deprecated as of NDB 8.0.23.

    For more information, see Section 23.7.11, 鈥淣DB Cluster Replication Conflict Resolution鈥?/a>.

  • ndb_data_node_neighbour

    Command-Line Format --ndb-data-node-neighbour=#
    System Variable ndb_data_node_neighbour
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Integer
    Default Value 0
    Minimum Value 0
    Maximum Value 255

    Sets the ID of a 鈥?span class="quote">nearest鈥?/span> data node鈥攖hat is, a preferred nonlocal data node is chosen to execute the transaction, rather than one running on the same host as the SQL or API node. This used to ensure that when a fully replicated table is accessed, we access it on this data node, to ensure that the local copy of the table is always used whenever possible. This can also be used for providing hints for transactions.

    This can improve data access times in the case of a node that is physically closer than and thus has higher network throughput than others on the same host.

    See Section 13.1.20.12, 鈥淪etting NDB Comment Options鈥?/a>, for further information.

    Note

    An equivalent method set_data_node_neighbour() is provided for use in NDB API applications.

  • ndb_dbg_check_shares

    Command-Line Format --ndb-dbg-check-shares=#
    Introduced 8.0.13-ndb-8.0.13
    System Variable ndb_dbg_check_shares
    Scope Global, Session
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Integer
    Default Value 0
    Minimum Value 0
    Maximum Value 1

    When set to 1, check that no shares are lingering. Available in debug builds only.

  • ndb_default_column_format

    Command-Line Format --ndb-default-column-format={FIXED|DYNAMIC}
    System Variable ndb_default_column_format
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Enumeration
    Default Value FIXED
    Valid Values

    FIXED

    DYNAMIC

    Sets the default COLUMN_FORMAT and ROW_FORMAT for new tables (see Section 13.1.20, 鈥淐REATE TABLE Statement鈥?/a>). The default is FIXED.

  • ndb_deferred_constraints

    Command-Line Format --ndb-deferred-constraints=#
    System Variable ndb_deferred_constraints
    Scope Global, Session
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Integer
    Default Value 0
    Minimum Value 0
    Maximum Value 1

    Controls whether or not constraint checks are deferred, where these are supported. 0 is the default.

    This variable is not normally needed for operation of NDB Cluster or NDB Cluster Replication, and is intended primarily for use in testing.

  • ndb_distribution

    Command-Line Format --ndb-distribution={KEYHASH|LINHASH}
    System Variable ndb_distribution
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Enumeration
    Default Value KEYHASH
    Valid Values

    LINHASH

    KEYHASH

    Controls the default distribution method for NDB tables. Can be set to either of KEYHASH (key hashing) or LINHASH (linear hashing). KEYHASH is the default.

  • ndb_eventbuffer_free_percent

    Command-Line Format --ndb-eventbuffer-free-percent=#
    System Variable ndb_eventbuffer_free_percent
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Integer
    Default Value 20
    Minimum Value 1
    Maximum Value 99

    Sets the percentage of the maximum memory allocated to the event buffer (ndb_eventbuffer_max_alloc) that should be available in event buffer after reaching the maximum, before starting to buffer again.

  • ndb_eventbuffer_max_alloc

    Command-Line Format --ndb-eventbuffer-max-alloc=#
    System Variable ndb_eventbuffer_max_alloc
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Integer
    Default Value 0
    Minimum Value 0
    Maximum Value (鈮?8.0.26-ndb-8.0.26) 9223372036854775807
    Maximum Value 9223372036854775807
    Maximum Value 9223372036854775807
    Maximum Value (鈮?8.0.25-ndb-8.0.25) 4294967295

    Sets the maximum amount memory (in bytes) that can be allocated for buffering events by the NDB API. 0 means that no limit is imposed, and is the default.

  • ndb_extra_logging

    Command-Line Format ndb_extra_logging=#
    System Variable ndb_extra_logging
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Integer
    Default Value 1
    Minimum Value 0
    Maximum Value 1

    This variable enables recording in the MySQL error log of information specific to the NDB storage engine.

    When this variable is set to 0, the only information specific to NDB that is written to the MySQL error log relates to transaction handling. If it set to a value greater than 0 but less than 10, NDB table schema and connection events are also logged, as well as whether or not conflict resolution is in use, and other NDB errors and information. If the value is set to 10 or more, information about NDB internals, such as the progress of data distribution among cluster nodes, is also written to the MySQL error log. The default is 1.

  • ndb_force_send

    Command-Line Format --ndb-force-send[={OFF|ON}]
    System Variable ndb_force_send
    Scope Global, Session
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Boolean
    Default Value ON

    Forces sending of buffers to NDB immediately, without waiting for other threads. Defaults to ON.

  • ndb_fully_replicated

    Command-Line Format --ndb-fully-replicated[={OFF|ON}]
    System Variable ndb_fully_replicated
    Scope Global, Session
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Boolean
    Default Value OFF

    Determines whether new NDB tables are fully replicated. This setting can be overridden for an individual table using COMMENT="NDB_TABLE=FULLY_REPLICATED=..." in a CREATE TABLE or ALTER TABLE statement; see Section 13.1.20.12, 鈥淪etting NDB Comment Options鈥?/a>, for syntax and other information.

  • ndb_index_stat_enable

    Command-Line Format --ndb-index-stat-enable[={OFF|ON}]
    System Variable ndb_index_stat_enable
    Scope Global, Session
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Boolean
    Default Value ON

    Use NDB index statistics in query optimization. The default is ON.

    Prior to NDB 8.0.27, starting the server with --ndb-index-stat-enable set to OFF prevented the creation of the index statistics tables. In NDB 8.0.27 and later, these tables are always created when the server starts, regardless of this option's value.

  • ndb_index_stat_option

    Command-Line Format --ndb-index-stat-option=value
    System Variable ndb_index_stat_option
    Scope Global, Session
    Dynamic Yes
    SET_VAR Hint Applies No
    Type String
    Default Value loop_checkon=1000ms,loop_idle=1000ms,loop_busy=100ms, update_batch=1,read_batch=4,idle_batch=32,check_batch=32, check_delay=1m,delete_batch=8,clean_delay=0,error_batch=4, error_delay=1m,evict_batch=8,evict_delay=1m,cache_limit=32M, cache_lowpct=90

    This variable is used for providing tuning options for NDB index statistics generation. The list consist of comma-separated name-value pairs of option names and values, and this list must not contain any space characters.

    Options not used when setting ndb_index_stat_option are not changed from their default values. For example, you can set ndb_index_stat_option = 'loop_idle=1000ms,cache_limit=32M'.

    Time values can be optionally suffixed with h (hours), m (minutes), or s (seconds). Millisecond values can optionally be specified using ms; millisecond values cannot be specified using h, m, or s.) Integer values can be suffixed with K, M, or G.

    The names of the options that can be set using this variable are shown in the table that follows. The table also provides brief descriptions of the options, their default values, and (where applicable) their minimum and maximum values.

    Table 23.20 ndb_index_stat_option options and values

    Name Description Default/Units Minimum/Maximum
    loop_enable 1000 ms 0/4G
    loop_idle Time to sleep when idle 1000 ms 0/4G
    loop_busy Time to sleep when more work is waiting 100 ms 0/4G
    update_batch 1 0/4G
    read_batch 4 1/4G
    idle_batch 32 1/4G
    check_batch 8 1/4G
    check_delay How often to check for new statistics 10 m 1/4G
    delete_batch 8 0/4G
    clean_delay 1 m 0/4G
    error_batch 4 1/4G
    error_delay 1 m 1/4G
    evict_batch 8 1/4G
    evict_delay Clean LRU cache, from read time 1 m 0/4G
    cache_limit Maximum amount of memory in bytes used for cached index statistics by this mysqld; clean up the cache when this is exceeded. 32 M 0/4G
    cache_lowpct 90 0/100
    zero_total Setting this to 1 resets all accumulating counters in ndb_index_stat_status to 0. This option value is also reset to 0 when this is done. 0 0/1
    Name Description Default/Units Minimum/Maximum

  • ndb_join_pushdown

    System Variable ndb_join_pushdown
    Scope Global, Session
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Boolean
    Default Value ON

    This variable controls whether joins on NDB tables are pushed down to the NDB kernel (data nodes). Previously, a join was handled using multiple accesses of NDB by the SQL node; however, when ndb_join_pushdown is enabled, a pushable join is sent in its entirety to the data nodes, where it can be distributed among the data nodes and executed in parallel on multiple copies of the data, with a single, merged result being returned to mysqld. This can reduce greatly the number of round trips between an SQL node and the data nodes required to handle such a join.

    By default, ndb_join_pushdown is enabled.

    Conditions for NDB pushdown joins.  In order for a join to be pushable, it must meet the following conditions:

    1. Only columns can be compared, and all columns to be joined must use exactly the same data type. This means that (for example) a join on an INT column and a BIGINT column also cannot be pushed down.

      Previously, expressions such as t1.a = t2.a + constant could not be pushed down. This restriction is lifted in NDB 8.0. The result of any operations on any column to be compared must yield the same type as the column itself.

      Expressions comparing columns from the same table can also be pushed down. The columns (or the result of any operations on those columns) must be of exactly the same type, including the same signedness, length, character set and collation, precision, and scale, where these are applicable.

    2. Queries referencing BLOB or TEXT columns are not supported.

    3. Explicit locking is not supported; however, the NDB storage engine's characteristic implicit row-based locking is enforced.

      This means that a join using FOR UPDATE cannot be pushed down.

    4. In order for a join to be pushed down, child tables in the join must be accessed using one of the ref, eq_ref, or  const access methods, or some combination of these methods.

      Outer joined child tables can only be pushed using eq_ref.

      If the root of the pushed join is an eq_ref or const, only child tables joined by eq_ref can be appended. (A table joined by ref is likely to become the root of another pushed join.)

      If the query optimizer decides on Using join cache for a candidate child table, that table cannot be pushed as a child. However, it may be the root of another set of pushed tables.

    5. Joins referencing tables explicitly partitioned by [LINEAR] HASH, LIST, or RANGE currently cannot be pushed down.

    You can see whether a given join can be pushed down by checking it with EXPLAIN; when the join can be pushed down, you can see references to the pushed join in the Extra column of the output, as shown in this example:

    Press CTRL+C to copy
    mysql> EXPLAIN -> SELECT e.first_name, e.last_name, t.title, d.dept_name -> FROM employees e -> JOIN dept_emp de ON e.emp_no=de.emp_no -> JOIN departments d ON d.dept_no=de.dept_no -> JOIN titles t ON e.emp_no=t.emp_no\G *************************** 1. row *************************** id: 1 select_type: SIMPLE table: d type: ALL possible_keys: PRIMARY key: NULL key_len: NULL ref: NULL rows: 9 Extra: Parent of 4 pushed join@1 *************************** 2. row *************************** id: 1 select_type: SIMPLE table: de type: ref possible_keys: PRIMARY,emp_no,dept_no key: dept_no key_len: 4 ref: employees.d.dept_no rows: 5305 Extra: Child of 'd' in pushed join@1 *************************** 3. row *************************** id: 1 select_type: SIMPLE table: e type: eq_ref possible_keys: PRIMARY key: PRIMARY key_len: 4 ref: employees.de.emp_no rows: 1 Extra: Child of 'de' in pushed join@1 *************************** 4. row *************************** id: 1 select_type: SIMPLE table: t type: ref possible_keys: PRIMARY,emp_no key: emp_no key_len: 4 ref: employees.de.emp_no rows: 19 Extra: Child of 'e' in pushed join@1 4 rows in set (0.00 sec)
    Note

    If inner joined child tables are joined by ref, and the result is ordered or grouped by a sorted index, this index cannot provide sorted rows, which forces writing to a sorted tempfile.

    Two additional sources of information about pushed join performance are available:

    1. The status variables Ndb_pushed_queries_defined, Ndb_pushed_queries_dropped, Ndb_pushed_queries_executed, and Ndb_pushed_reads.

    2. The counters in the ndbinfo.counters table that belong to the DBSPJ kernel block.

  • ndb_log_apply_status

    Command-Line Format --ndb-log-apply-status[={OFF|ON}]
    System Variable ndb_log_apply_status
    Scope Global
    Dynamic No
    SET_VAR Hint Applies No
    Type Boolean
    Default Value OFF

    A read-only variable which shows whether the server was started with the --ndb-log-apply-status option.

  • ndb_log_bin

    Command-Line Format --ndb-log-bin[={OFF|ON}]
    System Variable ndb_log_bin
    Scope Global, Session
    Dynamic No
    SET_VAR Hint Applies No
    Type Boolean
    Default Value (鈮?8.0.16-ndb-8.0.16) OFF
    Default Value (鈮?8.0.15-ndb-8.0.15) ON

    Causes updates to NDB tables to be written to the binary log. The setting for this variable has no effect if binary logging is not already enabled on the server using log_bin. In NDB 8.0, ndb_log_bin defaults to 0 (FALSE).

  • ndb_log_binlog_index

    Command-Line Format --ndb-log-binlog-index[={OFF|ON}]
    System Variable ndb_log_binlog_index
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Boolean
    Default Value ON

    Causes a mapping of epochs to positions in the binary log to be inserted into the ndb_binlog_index table. Setting this variable has no effect if binary logging is not already enabled for the server using log_bin. (In addition, ndb_log_bin must not be disabled.) ndb_log_binlog_index defaults to 1 (ON); normally, there is never any need to change this value in a production environment.

  • ndb_log_empty_epochs

    Command-Line Format --ndb-log-empty-epochs[={OFF|ON}]
    System Variable ndb_log_empty_epochs
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Boolean
    Default Value OFF

    When this variable is set to 0, epoch transactions with no changes are not written to the binary log, although a row is still written even for an empty epoch in ndb_binlog_index.

  • ndb_log_empty_update

    Command-Line Format --ndb-log-empty-update[={OFF|ON}]
    System Variable ndb_log_empty_update
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Boolean
    Default Value OFF

    When this variable is set to ON (1), update transactions with no changes are written to the binary log, even when log_replica_updates or log_slave_updates is enabled.

  • ndb_log_exclusive_reads

    Command-Line Format --ndb-log-exclusive-reads[={OFF|ON}]
    System Variable ndb_log_exclusive_reads
    Scope Global, Session
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Boolean
    Default Value 0

    This variable determines whether primary key reads are logged with exclusive locks, which allows for NDB Cluster Replication conflict detection and resolution based on read conflicts. To enable these locks, set the value of ndb_log_exclusive_reads to 1. 0, which disables such locking, is the default.

    For more information, see Read conflict detection and resolution.

  • ndb_log_orig

    Command-Line Format --ndb-log-orig[={OFF|ON}]
    System Variable ndb_log_orig
    Scope Global
    Dynamic No
    SET_VAR Hint Applies No
    Type Boolean
    Default Value OFF

    Shows whether the originating server ID and epoch are logged in the ndb_binlog_index table. Set using the --ndb-log-orig server option.

  • ndb_log_transaction_id

    System Variable ndb_log_transaction_id
    Scope Global
    Dynamic No
    SET_VAR Hint Applies No
    Type Boolean
    Default Value OFF

    This read-only, Boolean system variable shows whether a replica mysqld writes NDB transaction IDs in the binary log (required to use 鈥?span class="quote">active-active鈥?/span> NDB Cluster Replication with NDB$EPOCH_TRANS() conflict detection). To change the setting, use the --ndb-log-transaction-id option.

    ndb_log_transaction_id is not supported in mainline MySQL Server 8.0.

    For more information, see Section 23.7.11, 鈥淣DB Cluster Replication Conflict Resolution鈥?/a>.

  • ndb_log_transaction_compression

    Command-Line Format --ndb-log-transaction-compression
    Introduced 8.0.31-ndb-8.0.31
    System Variable ndb_log_transaction_compression
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Boolean
    Default Value OFF

    Whether a replica mysqld writes compressed transactions in the binary log; present only if mysqld was compiled with support for NDB.

    You should note that starting the MySQL server with --binlog-transaction-compression forces this variable to be enabled (ON), and that this overrides any setting for --ndb-log-transaction-compression made on the command line or in a my.cnf file, as shown here:

    Press CTRL+C to copy
    $> mysqld_safe --ndbcluster --ndb-connectstring=127.0.0.1 \ --binlog-transaction-compression=ON --ndb-log-transaction-compression=OFF & [1] 27667 $> 2022-07-07T12:29:20.459937Z mysqld_safe Logging to '/usr/local/mysql/data/myhost.err'. 2022-07-07T12:29:20.509873Z mysqld_safe Starting mysqld daemon with databases from /usr/local/mysql/data $> mysql -e 'SHOW VARIABLES LIKE "%transaction_compression%"' +--------------------------------------------+-------+ | Variable_name | Value | +--------------------------------------------+-------+ | binlog_transaction_compression | ON | | binlog_transaction_compression_level_zstd | 3 | | ndb_log_transaction_compression | ON | | ndb_log_transaction_compression_level_zstd | 3 | +--------------------------------------------+-------+

    To disable binary log transaction compression for NDB tables only, set the ndb_log_transaction_compression system variable to OFF in a mysql or other client session after starting mysqld.

    Setting the binlog_transaction_compression variable after startup has no effect on the value of ndb_log_transaction_compression.

    For more information on binary log transaction compression, such as which events are or are not compressed and as well as behavior changes to be aware of when this feature is used, see Section 5.4.4.5, 鈥淏inary Log Transaction Compression鈥?/a>.

  • ndb_log_transaction_compression_level_zstd

    Command-Line Format --ndb-log-transaction-compression-level-zstd=#
    Introduced 8.0.31-ndb-8.0.31
    System Variable ndb_log_transaction_compression_level_zstd
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Integer
    Default Value 3
    Minimum Value 1
    Maximum Value 22

    The ZSTD compression level used for writing compressed transactions to the replica's binary log if enabled by ndb_log_transaction_compression. Not supported if mysqld was not compiled with support for the NDB storage engine.

    See Section 5.4.4.5, 鈥淏inary Log Transaction Compression鈥?/a>, for more information.

  • ndb_metadata_check

    Command-Line Format --ndb-metadata-check[={OFF|ON}]
    Introduced 8.0.16-ndb-8.0.16
    System Variable ndb_metadata_check
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Boolean
    Default Value ON

    NDB uses a background thread to check for metadata changes each ndb_metadata_check_interval seconds as compared with the MySQL data dictionary. This metadata change detection thread can be disabled by setting ndb_metadata_check to OFF. The thread is enabled by default.

  • ndb_metadata_check_interval

    Command-Line Format --ndb-metadata-check-interval=#
    Introduced 8.0.16-ndb-8.0.16
    System Variable ndb_metadata_check_interval
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Integer
    Default Value 60
    Minimum Value 0
    Maximum Value 31536000
    Unit seconds

    NDB runs a metadata change detection thread in the background to determine when the NDB dictionary has changed with respect to the MySQL data dictionary. By default,the interval between such checks is 60 seconds; this can be adjusted by setting the value of ndb_metadata_check_interval. To enable or disable the thread, use ndb_metadata_check.

  • ndb_metadata_sync

    Introduced 8.0.19-ndb-8.0.19
    System Variable ndb_metadata_sync
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Boolean
    Default Value false

    Setting this variable causes the change monitor thread to override any values set for ndb_metadata_check or ndb_metadata_check_interval, and to enter a period of continuous change detection. When the thread ascertains that there are no more changes to be detected, it stalls until the binary logging thread has finished synchronization of all detected objects. ndb_metadata_sync is then set to false, and the change monitor thread reverts to the behavior determined by the settings for ndb_metadata_check and ndb_metadata_check_interval.

    In NDB 8.0.22 and later, setting this variable to true causes the list of excluded objects to be cleared, and setting it to false clears the list of objects to be retried.

  • ndb_optimized_node_selection

    Command-Line Format --ndb-optimized-node-selection=#
    System Variable ndb_optimized_node_selection
    Scope Global
    Dynamic No
    SET_VAR Hint Applies No
    Type Integer
    Default Value 3
    Minimum Value 0
    Maximum Value 3

    There are two forms of optimized node selection, described here:

    1. The SQL node uses promixity to determine the transaction coordinator; that is, the 鈥?span class="quote">closest鈥?/span> data node to the SQL node is chosen as the transaction coordinator. For this purpose, a data node having a shared memory connection with the SQL node is considered to be 鈥?span class="quote">closest鈥?/span> to the SQL node; the next closest (in order of decreasing proximity) are: TCP connection to localhost, followed by TCP connection from a host other than localhost.

    2. The SQL thread uses distribution awareness to select the data node. That is, the data node housing the cluster partition accessed by the first statement of a given transaction is used as the transaction coordinator for the entire transaction. (This is effective only if the first statement of the transaction accesses no more than one cluster partition.)

    This option takes one of the integer values 0, 1, 2, or 3. 3 is the default. These values affect node selection as follows:

    • 0: Node selection is not optimized. Each data node is employed as the transaction coordinator 8 times before the SQL thread proceeds to the next data node.

    • 1: Proximity to the SQL node is used to determine the transaction coordinator.

    • 2: Distribution awareness is used to select the transaction coordinator. However, if the first statement of the transaction accesses more than one cluster partition, the SQL node reverts to the round-robin behavior seen when this option is set to 0.

    • 3: If distribution awareness can be employed to determine the transaction coordinator, then it is used; otherwise proximity is used to select the transaction coordinator. (This is the default behavior.)

    Proximity is determined as follows:

    1. Start with the value set for the Group parameter (default 55).

    2. For an API node sharing the same host with other API nodes, decrement the value by 1. Assuming the default value for Group, the effective value for data nodes on same host as the API node is 54, and for remote data nodes 55.

    3. Setting ndb_data_node_neighbour further decreases the effective Group value by 50, causing this node to be regarded as the nearest node. This is needed only when all data nodes are on hosts other than that hosts the API node and it is desirable to dedicate one of them to the API node. In normal cases, the default adjustment described previously is sufficient.

    Frequent changes in ndb_data_node_neighbour are not advisable, since this changes the state of the cluster connection and thus may disrupt the selection algorithm for new transactions from each thread until it stablilizes.

  • ndb_read_backup

    Command-Line Format --ndb-read-backup[={OFF|ON}]
    System Variable ndb_read_backup
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Boolean
    Default Value (鈮?8.0.19-ndb-8.0.19) ON
    Default Value (鈮?8.0.18-ndb-8.0.18) OFF

    Enable read from any fragment replica for any NDB table subsequently created; doing so greatly improves the table read performance at a relatively small cost to writes.

    If the SQL node and the data node use the same host name or IP address, this fact is detected automatically, so that the preference is to send reads to the same host. If these nodes are on the same host but use different IP addresses, you can tell the SQL node to use the correct data node by setting the value of ndb_data_node_neighbour on the SQL node to the node ID of the data node.

    To enable or disable read from any fragment replica for an individual table, you can set the NDB_TABLE option READ_BACKUP for the table accordingly, in a CREATE TABLE or ALTER TABLE statement; see Section 13.1.20.12, 鈥淪etting NDB Comment Options鈥?/a>, for more information.

  • ndb_recv_thread_activation_threshold

    Command-Line Format --ndb-recv-thread-activation-threshold=#
    System Variable ndb_recv_thread_activation_threshold
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Integer
    Default Value 8
    Minimum Value 0 (MIN_ACTIVATION_THRESHOLD)
    Maximum Value 16 (MAX_ACTIVATION_THRESHOLD)

    When this number of concurrently active threads is reached, the receive thread takes over polling of the cluster connection.

    This variable is global in scope. It can also be set at startup.

  • ndb_recv_thread_cpu_mask

    Command-Line Format --ndb-recv-thread-cpu-mask=mask
    System Variable ndb_recv_thread_cpu_mask
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Bitmap
    Default Value [empty]

    CPU mask for locking receiver threads to specific CPUs. This is specified as a hexadecimal bitmask. For example, 0x33 means that one CPU is used per receiver thread. An empty string is the default; setting ndb_recv_thread_cpu_mask to this value removes any receiver thread locks previously set.

    This variable is global in scope. It can also be set at startup.

  • ndb_report_thresh_binlog_epoch_slip

    Command-Line Format --ndb-report-thresh-binlog-epoch-slip=#
    System Variable ndb_report_thresh_binlog_epoch_slip
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Integer
    Default Value 10
    Minimum Value 0
    Maximum Value 256

    This represents the threshold for the number of epochs completely buffered in the event buffer, but not yet consumed by the binlog injector thread. When this degree of slippage (lag) is exceeded, an event buffer status message is reported, with BUFFERED_EPOCHS_OVER_THRESHOLD supplied as the reason (see Section 23.6.2.3, 鈥淓vent Buffer Reporting in the Cluster Log鈥?/a>). Slip is increased when an epoch is received from data nodes and buffered completely in the event buffer; it is decreased when an epoch is consumed by the binlog injector thread, it is reduced. Empty epochs are buffered and queued, and so included in this calculation only when this is enabled using the Ndb::setEventBufferQueueEmptyEpoch() method from the NDB API.

  • ndb_report_thresh_binlog_mem_usage

    Command-Line Format --ndb-report-thresh-binlog-mem-usage=#
    System Variable ndb_report_thresh_binlog_mem_usage
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Integer
    Default Value 10
    Minimum Value 0
    Maximum Value 10

    This is a threshold on the percentage of free memory remaining before reporting binary log status. For example, a value of 10 (the default) means that if the amount of available memory for receiving binary log data from the data nodes falls below 10%, a status message is sent to the cluster log.

  • ndb_row_checksum

    System Variable ndb_row_checksum
    Scope Global, Session
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Integer
    Default Value 1
    Minimum Value 0
    Maximum Value 1

    Traditionally, NDB has created tables with row checksums, which checks for hardware issues at the expense of performance. Setting ndb_row_checksum to 0 means that row checksums are not used for new or altered tables, which has a significant impact on performance for all types of queries. This variable is set to 1 by default, to provide backward-compatible behavior.

  • ndb_schema_dist_lock_wait_timeout

    Command-Line Format --ndb-schema-dist-lock-wait-timeout=value
    Introduced 8.0.18-ndb-8.0.18
    System Variable ndb_schema_dist_lock_wait_timeout
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Integer
    Default Value 30
    Minimum Value 0
    Maximum Value 1200
    Unit seconds

    Number of seconds to wait during schema distribution for the metadata lock taken on each SQL node in order to change its local data dictionary to reflect the DDL statement change. After this time has elapsed, a warning is returned to the effect that a given SQL node's data dictionary was not updated with the change. This avoids having the binary logging thread wait an excessive length of time while handling schema operations.

  • ndb_schema_dist_timeout

    Command-Line Format --ndb-schema-dist-timeout=value
    Introduced 8.0.16-ndb-8.0.16
    System Variable ndb_schema_dist_timeout
    Scope Global
    Dynamic No
    SET_VAR Hint Applies No
    Type Integer
    Default Value 120
    Minimum Value 5
    Maximum Value 1200
    Unit seconds

    Number of seconds to wait before detecting a timeout during schema distribution. This can indicate that other SQL nodes are experiencing excessive activity, or that they are somehow being prevented from acquiring necessary resources at this time.

  • ndb_schema_dist_upgrade_allowed

    Command-Line Format --ndb-schema-dist-upgrade-allowed=value
    Introduced 8.0.17-ndb-8.0.17
    System Variable ndb_schema_dist_upgrade_allowed
    Scope Global
    Dynamic No
    SET_VAR Hint Applies No
    Type Boolean
    Default Value true

    Allow upgrading of the schema distribution table when connecting to NDB. When true (the default), this change is deferred until all SQL nodes have been upgraded to the same version of the NDB Cluster software.

    Note

    The performance of the schema distribution may be somewhat degraded until the upgrade has been performed.

  • ndb_show_foreign_key_mock_tables

    Command-Line Format --ndb-show-foreign-key-mock-tables[={OFF|ON}]
    System Variable ndb_show_foreign_key_mock_tables
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Boolean
    Default Value OFF

    Show the mock tables used by NDB to support foreign_key_checks=0. When this is enabled, extra warnings are shown when creating and dropping the tables. The real (internal) name of the table can be seen in the output of SHOW CREATE TABLE.

  • ndb_slave_conflict_role

    Command-Line Format --ndb-slave-conflict-role=value
    Deprecated 8.0.23-ndb-8.0.23
    System Variable ndb_slave_conflict_role
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Enumeration
    Default Value NONE
    Valid Values

    NONE

    PRIMARY

    SECONDARY

    PASS

    Deprecated in NDB 8.0.23, and subject to removal in a future release. Use ndb_conflict_role instead.

  • ndb_table_no_logging

    System Variable ndb_table_no_logging
    Scope Session
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Boolean
    Default Value OFF

    When this variable is set to ON or 1, it causes NDB tables not to be checkpointed to disk. More specifically, this setting applies to tables which are created or altered using ENGINE NDB when ndb_table_no_logging is enabled, and continues to apply for the lifetime of the table, even if ndb_table_no_logging is later changed. Suppose that A, B, C, and D are tables that we create (and perhaps also alter), and that we also change the setting for ndb_table_no_logging as shown here:

    Press CTRL+C to copy
    SET @@ndb_table_no_logging = 1; CREATE TABLE A ... ENGINE NDB; CREATE TABLE B ... ENGINE MYISAM; CREATE TABLE C ... ENGINE MYISAM; ALTER TABLE B ENGINE NDB; SET @@ndb_table_no_logging = 0; CREATE TABLE D ... ENGINE NDB; ALTER TABLE C ENGINE NDB; SET @@ndb_table_no_logging = 1;

    After the previous sequence of events, tables A and B are not checkpointed; A was created with ENGINE NDB and B was altered to use NDB, both while ndb_table_no_logging was enabled. However, tables C and D are logged; C was altered to use NDB and D was created using ENGINE NDB, both while ndb_table_no_logging was disabled. Setting ndb_table_no_logging back to 1 or ON does not cause table C or D to be checkpointed.

    Note

    ndb_table_no_logging has no effect on the creation of NDB table schema files; to suppress these, use ndb_table_temporary instead.

  • ndb_table_temporary

    System Variable ndb_table_temporary
    Scope Session
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Boolean
    Default Value OFF

    When set to ON or 1, this variable causes NDB tables not to be written to disk: This means that no table schema files are created, and that the tables are not logged.

    Note

    Setting this variable currently has no effect. This is a known issue; see Bug #34036.

  • ndb_use_copying_alter_table

    System Variable ndb_use_copying_alter_table
    Scope Global, Session
    Dynamic No
    SET_VAR Hint Applies No

    Forces NDB to use copying of tables in the event of problems with online ALTER TABLE operations. The default value is OFF.

  • ndb_use_exact_count

    System Variable ndb_use_exact_count
    Scope Global, Session
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Boolean
    Default Value OFF

    Forces NDB to use a count of records during SELECT COUNT(*) query planning to speed up this type of query. The default value is OFF, which allows for faster queries overall.

  • ndb_use_transactions

    Command-Line Format --ndb-use-transactions[={OFF|ON}]
    System Variable ndb_use_transactions
    Scope Global, Session
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Boolean
    Default Value ON

    You can disable NDB transaction support by setting this variable's value to OFF. This is generally not recommended, although it may be useful to disable transaction support within a given client session when that session is used to import one or more dump files with large transactions; this allows a multi-row insert to be executed in parts, rather than as a single transaction. In such cases, once the import has been completed, you should either reset the variable value for this session to ON, or simply terminate the session.

  • ndb_version

    System Variable ndb_version
    Scope Global
    Dynamic No
    SET_VAR Hint Applies No
    Type String
    Default Value

    NDB engine version, as a composite integer.

  • ndb_version_string

    System Variable ndb_version_string
    Scope Global
    Dynamic No
    SET_VAR Hint Applies No
    Type String
    Default Value

    NDB engine version in ndb-x.y.z format.

  • replica_allow_batching

    Command-Line Format --replica-allow-batching[={OFF|ON}]
    Introduced 8.0.26-ndb-8.0.26
    System Variable replica_allow_batching
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Boolean
    Default Value (鈮?8.0.30-ndb-8.0.30) ON
    Default Value (鈮?8.0.29-ndb-8.0.29) OFF

    Whether or not batched updates are enabled on NDB Cluster replicas. Beginning with NDB 8.0.26, you should use replica_allow_batching in place of slave_allow_batching, which is deprecated in that release.

    Allowing batched updates on the replica greatly improves performance, particularly when replicating TEXT, BLOB, and JSON columns. For this reason, replica_allow_batching is enabled by default in NDB 8.0.30 and later.

    Setting this variable has an effect only when using replication with the NDB storage engine; in MySQL Server 8.0, it is present but does nothing. For more information, see Section 23.7.6, 鈥淪tarting NDB Cluster Replication (Single Replication Channel)鈥?/a>.

  • ndb_replica_batch_size

    Command-Line Format --ndb-replica-batch-size=#
    Introduced 8.0.30-ndb-8.0.30
    System Variable ndb_replica_batch_size
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Integer
    Default Value 2097152
    Minimum Value 0
    Maximum Value 2097152
    Unit bytes

    Determines the batch size in bytes used for writes applied on the replica. In NDB 8.0.30 and later, set this variable rather than the --ndb-batch-size option to apply this setting to the replica, exclusive of any other sessions.

  • ndb_replica_blob_write_batch_bytes

    Command-Line Format --ndb-replica-blob-write-batch-bytes=#
    Introduced 8.0.30-ndb-8.0.30
    System Variable ndb_replica_blob_write_batch_bytes
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Integer
    Default Value 2097152
    Minimum Value 0
    Maximum Value 2097152
    Unit bytes

    Control the batch write size used for blob data by the replication applier.

    Beginning with NDB 8.0.30, you should set this variable rather than the --ndb-blob-write-batch-bytes option to control the blob batch write size on the replica, exclusive of any other sessions. The reason for this is that, when ndb_replica_blob_write_batch_bytes鈥媔s not set,鈥媡he effective blob batch size (that is, the maximum number of pending bytes to write for blob columns) is determined by the maximum of the default value of ndb_replica_blob_write_batch_bytes and the value set for --ndb-blob-write-batch-bytes.

    Setting ndb_replica_blob_write_batch_bytes to 0 means that NDB imposes no limit on the size of blob batch writes on the replica.

  • server_id_bits

    Command-Line Format --server-id-bits=#
    System Variable server_id_bits
    Scope Global
    Dynamic No
    SET_VAR Hint Applies No
    Type Integer
    Default Value 32
    Minimum Value 7
    Maximum Value 32

    This variable indicates the number of least significant bits within the 32-bit server_id which actually identify the server. Indicating that the server is actually identified by fewer than 32 bits makes it possible for some of the remaining bits to be used for other purposes, such as storing user data generated by applications using the NDB API's Event API within the AnyValue of an OperationOptions structure (NDB Cluster uses the AnyValue to store the server ID).

    When extracting the effective server ID from server_id for purposes such as detection of replication loops, the server ignores the remaining bits. The server_id_bits variable is used to mask out any irrelevant bits of server_id in the I/O and SQL threads when deciding whether an event should be ignored based on the server ID.

    This data can be read from the binary log by mysqlbinlog, provided that it is run with its own server_id_bits variable set to 32 (the default).

    If the value of server_id greater than or equal to 2 to the power of server_id_bits; otherwise, mysqld refuses to start.

    This system variable is supported only by NDB Cluster. It is not supported in the standard MySQL 8.0 Server.

  • slave_allow_batching

    Command-Line Format --slave-allow-batching[={OFF|ON}]
    Deprecated 8.0.26-ndb-8.0.26
    System Variable slave_allow_batching
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Boolean
    Default Value (鈮?8.0.30-ndb-8.0.30) ON
    Default Value (鈮?8.0.29-ndb-8.0.29) OFF

    Whether or not batched updates are enabled on NDB Cluster replicas. Beginning with NDB 8.0.26, this variable is deprecated, and you should use replica_allow_batching instead.

    Allowing batched updates on the replica greatly improves performance, particularly when replicating TEXT, BLOB, and JSON columns. For this reason, replica_allow_batching is ON by default in NDB 8.0.30 and later. Also beginning with NDB 8.0.30, a warning is issued whenever this variable is set to OFF.

    Setting this variable has an effect only when using replication with the NDB storage engine; in MySQL Server 8.0, it is present but does nothing. For more information, see Section 23.7.6, 鈥淪tarting NDB Cluster Replication (Single Replication Channel)鈥?/a>.

  • transaction_allow_batching

    System Variable transaction_allow_batching
    Scope Session
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Boolean
    Default Value OFF

    When set to 1 or ON, this variable enables batching of statements within the same transaction. To use this variable, autocommit must first be disabled by setting it to 0 or OFF; otherwise, setting transaction_allow_batching has no effect.

    It is safe to use this variable with transactions that performs writes only, as having it enabled can lead to reads from the 鈥?span class="quote">before鈥?/span> image. You should ensure that any pending transactions are committed (using an explicit COMMIT if desired) before issuing a SELECT.

    Important

    transaction_allow_batching should not be used whenever there is the possibility that the effects of a given statement depend on the outcome of a previous statement within the same transaction.

    This variable is currently supported for NDB Cluster only.

The system variables in the following list all relate to the ndbinfo information database.

  • ndbinfo_database

    System Variable ndbinfo_database
    Scope Global
    Dynamic No
    SET_VAR Hint Applies No
    Type String
    Default Value ndbinfo

    Shows the name used for the NDB information database; the default is ndbinfo. This is a read-only variable whose value is determined at compile time.

  • ndbinfo_max_bytes

    Command-Line Format --ndbinfo-max-bytes=#
    System Variable ndbinfo_max_bytes
    Scope Global, Session
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Integer
    Default Value 0
    Minimum Value 0
    Maximum Value 65535

    Used in testing and debugging only.

  • ndbinfo_max_rows

    Command-Line Format --ndbinfo-max-rows=#
    System Variable ndbinfo_max_rows
    Scope Global, Session
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Integer
    Default Value 10
    Minimum Value 1
    Maximum Value 256

    Used in testing and debugging only.

  • ndbinfo_offline

    System Variable ndbinfo_offline
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Boolean
    Default Value OFF

    Place the ndbinfo database into offline mode, in which tables and views can be opened even when they do not actually exist, or when they exist but have different definitions in NDB. No rows are returned from such tables (or views).

  • ndbinfo_show_hidden

    Command-Line Format --ndbinfo-show-hidden[={OFF|ON}]
    System Variable ndbinfo_show_hidden
    Scope Global, Session
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Boolean
    Default Value OFF
    Valid Values

    ON

    OFF

    Whether or not the ndbinfo database's underlying internal tables are shown in the mysql client. The default is OFF.

    Note

    When ndbinfo_show_hidden is enabled, the internal tables are shown in the ndbinfo database only; they are not visible in TABLES or other INFORMATION_SCHEMA tables, regardless of the variable's setting.

  • ndbinfo_table_prefix

    System Variable ndbinfo_table_prefix
    Scope Global
    Dynamic No
    SET_VAR Hint Applies No
    Type String
    Default Value ndb$

    The prefix used in naming the ndbinfo database's base tables (normally hidden, unless exposed by setting ndbinfo_show_hidden). This is a read-only variable whose default value is ndb$; the prefix itself is determined at compile time.

  • ndbinfo_version

    System Variable ndbinfo_version
    Scope Global
    Dynamic No
    SET_VAR Hint Applies No
    Type String
    Default Value

    Shows the version of the ndbinfo engine in use; read-only.

23.4.3.9.3 NDB Cluster Status Variables

This section provides detailed information about MySQL server status variables that relate to NDB Cluster and the NDB storage engine. For status variables not specific to NDB Cluster, and for general information on using status variables, see Section 5.1.10, 鈥淪erver Status Variables鈥?/a>.


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MySQL 8.0 Reference Manual  /  ...  /  Password Validation Options and Variables

6.4.3.2 Password Validation Options and Variables

This section describes the system and status variables that validate_password provides to enable its operation to be configured and monitored.

Password Validation Component System Variables

If the validate_password component is enabled, it exposes several system variables that enable configuration of password checking:

mysql> SHOW VARIABLES LIKE 'validate_password.%';
+--------------------------------------+--------+
| Variable_name                        | Value  |
+--------------------------------------+--------+
| validate_password.check_user_name    | ON     |
| validate_password.dictionary_file    |        |
| validate_password.length             | 8      |
| validate_password.mixed_case_count   | 1      |
| validate_password.number_count       | 1      |
| validate_password.policy             | MEDIUM |
| validate_password.special_char_count | 1      |
+--------------------------------------+--------+

To change how passwords are checked, you can set these system variables at server startup or at runtime. The following list describes the meaning of each variable.

  • validate_password.check_user_name

    Command-Line Format --validate-password.check-user-name[={OFF|ON}]
    System Variable validate_password.check_user_name
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Boolean
    Default Value ON

    Whether validate_password compares passwords to the user name part of the effective user account for the current session and rejects them if they match. This variable is unavailable unless validate_password is installed.

    By default, validate_password.check_user_name is enabled. This variable controls user name matching independent of the value of validate_password.policy.

    When validate_password.check_user_name is enabled, it has these effects:

    • Checking occurs in all contexts for which validate_password is invoked, which includes use of statements such as ALTER USER or SET PASSWORD to change the current user's password, and invocation of functions such as VALIDATE_PASSWORD_STRENGTH().

    • The user names used for comparison are taken from the values of the USER() and CURRENT_USER() functions for the current session. An implication is that a user who has sufficient privileges to set another user's password can set the password to that user's name, and cannot set that user's password to the name of the user executing the statement. For example, 'root'@'localhost' can set the password for 'jeffrey'@'localhost' to 'jeffrey', but cannot set the password to 'root.

    • Only the user name part of the USER() and CURRENT_USER() function values is used, not the host name part. If a user name is empty, no comparison occurs.

    • If a password is the same as the user name or its reverse, a match occurs and the password is rejected.

    • User-name matching is case-sensitive. The password and user name values are compared as binary strings on a byte-by-byte basis.

    • If a password matches the user name, VALIDATE_PASSWORD_STRENGTH() returns 0 regardless of how other validate_password system variables are set.

  • validate_password.dictionary_file

    Command-Line Format --validate-password.dictionary-file=file_name
    System Variable validate_password.dictionary_file
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type File name

    The path name of the dictionary file that validate_password uses for checking passwords. This variable is unavailable unless validate_password is installed.

    By default, this variable has an empty value and dictionary checks are not performed. For dictionary checks to occur, the variable value must be nonempty. If the file is named as a relative path, it is interpreted relative to the server data directory. File contents should be lowercase, one word per line. Contents are treated as having a character set of utf8mb3. The maximum permitted file size is 1MB.

    For the dictionary file to be used during password checking, the password policy must be set to 2 (STRONG); see the description of the validate_password.policy system variable. Assuming that is true, each substring of the password of length 4 up to 100 is compared to the words in the dictionary file. Any match causes the password to be rejected. Comparisons are not case-sensitive.

    For VALIDATE_PASSWORD_STRENGTH(), the password is checked against all policies, including STRONG, so the strength assessment includes the dictionary check regardless of the validate_password.policy value.

    validate_password.dictionary_file can be set at runtime and assigning a value causes the named file to be read without a server restart.

  • validate_password.length

    Command-Line Format --validate-password.length=#
    System Variable validate_password.length
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Integer
    Default Value 8
    Minimum Value 0

    The minimum number of characters that validate_password requires passwords to have. This variable is unavailable unless validate_password is installed.

    The validate_password.length minimum value is a function of several other related system variables. The value cannot be set less than the value of this expression:

    Press CTRL+C to copy
    validate_password.number_count + validate_password.special_char_count + (2 * validate_password.mixed_case_count)

    If validate_password adjusts the value of validate_password.length due to the preceding constraint, it writes a message to the error log.

  • validate_password.mixed_case_count

    Command-Line Format --validate-password.mixed-case-count=#
    System Variable validate_password.mixed_case_count
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Integer
    Default Value 1
    Minimum Value 0

    The minimum number of lowercase and uppercase characters that validate_password requires passwords to have if the password policy is MEDIUM or stronger. This variable is unavailable unless validate_password is installed.

    For a given validate_password.mixed_case_count value, the password must have that many lowercase characters, and that many uppercase characters.

  • validate_password.number_count

    Command-Line Format --validate-password.number-count=#
    System Variable validate_password.number_count
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Integer
    Default Value 1
    Minimum Value 0

    The minimum number of numeric (digit) characters that validate_password requires passwords to have if the password policy is MEDIUM or stronger. This variable is unavailable unless validate_password is installed.

  • validate_password.policy

    Command-Line Format --validate-password.policy=value
    System Variable validate_password.policy
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Enumeration
    Default Value 1
    Valid Values

    0

    1

    2

    The password policy enforced by validate_password. This variable is unavailable unless validate_password is installed.

    validate_password.policy affects how validate_password uses its other policy-setting system variables, except for checking passwords against user names, which is controlled independently by validate_password.check_user_name.

    The validate_password.policy value can be specified using numeric values 0, 1, 2, or the corresponding symbolic values LOW, MEDIUM, STRONG. The following table describes the tests performed for each policy. For the length test, the required length is the value of the validate_password.length system variable. Similarly, the required values for the other tests are given by other validate_password.xxx variables.

    Policy Tests Performed
    0 or LOW Length
    1 or MEDIUM Length; numeric, lowercase/uppercase, and special characters
    2 or STRONG Length; numeric, lowercase/uppercase, and special characters; dictionary file
  • validate_password.special_char_count

    Command-Line Format --validate-password.special-char-count=#
    System Variable validate_password.special_char_count
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Integer
    Default Value 1
    Minimum Value 0

    The minimum number of nonalphanumeric characters that validate_password requires passwords to have if the password policy is MEDIUM or stronger. This variable is unavailable unless validate_password is installed.

Password Validation Component Status Variables

If the validate_password component is enabled, it exposes status variables that provide operational information:

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mysql> SHOW STATUS LIKE 'validate_password.%'; +-----------------------------------------------+---------------------+ | Variable_name | Value | +-----------------------------------------------+---------------------+ | validate_password.dictionary_file_last_parsed | 2019-10-03 08:33:49 | | validate_password.dictionary_file_words_count | 1902 | +-----------------------------------------------+---------------------+

The following list describes the meaning of each status variable.

Password Validation Plugin Options
Note

In MySQL 8.0, the validate_password plugin was reimplemented as the validate_password component. The validate_password plugin is deprecated; expect it to be removed in a future version of MySQL. Consequently, its options are also deprecated, and you should expect them to be removed as well. MySQL installations that use the plugin should make the transition to using the component instead. See Section 6.4.3.3, 鈥淭ransitioning to the Password Validation Component鈥?/a>.

To control activation of the validate_password plugin, use this option:

Password Validation Plugin System Variables
Note

In MySQL 8.0, the validate_password plugin was reimplemented as the validate_password component. The validate_password plugin is deprecated; expect it to be removed in a future version of MySQL. Consequently, its system variables are also deprecated and you should expect them to be removed as well. Use the corresponding system variables of the validate_password component instead; see Password Validation Component System Variables. MySQL installations that use the plugin should make the transition to using the component instead. See Section 6.4.3.3, 鈥淭ransitioning to the Password Validation Component鈥?/a>.

Password Validation Plugin Status Variables
Note

In MySQL 8.0, the validate_password plugin was reimplemented as the validate_password component. The validate_password plugin is deprecated; expect it to be removed in a future version of MySQL. Consequently, its status variables are also deprecated; expect it to be removed. Use the corresponding status variables of the validate_password component; see Password Validation Component Status Variables. MySQL installations that use the plugin should make the transition to using the component instead. See Section 6.4.3.3, 鈥淭ransitioning to the Password Validation Component鈥?/a>.


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MySQL 8.0 Reference Manual  /  MySQL Performance Schema  /  Performance Schema System Variables

27.15 Performance Schema System Variables

The Performance 鍥惧紡瀹炵幇several system variables that provide configuration information:

mysql> SHOW VARIABLES LIKE 'perf%';
+----------------------------------------------------------+-------+
| Variable_name                                            | Value |
+----------------------------------------------------------+-------+
| performance_schema                                       | ON    |
| performance_schema_accounts_size                         | -1    |
| performance_schema_digests_size                          | 10000 |
| performance_schema_events_stages_history_long_size       | 10000 |
| performance_schema_events_stages_history_size            | 10    |
| performance_schema_events_statements_history_long_size   | 10000 |
| performance_schema_events_statements_history_size        | 10    |
| performance_schema_events_transactions_history_long_size | 10000 |
| performance_schema_events_transactions_history_size      | 10    |
| performance_schema_events_waits_history_long_size        | 10000 |
| performance_schema_events_waits_history_size             | 10    |
| performance_schema_hosts_size                            | -1    |
| performance_schema_max_cond_classes                      | 80    |
| performance_schema_max_cond_instances                    | -1    |
| performance_schema_max_digest_length                     | 1024  |
| performance_schema_max_file_classes                      | 50    |
| performance_schema_max_file_handles                      | 32768 |
| performance_schema_max_file_instances                    | -1    |
| performance_schema_max_index_stat                        | -1    |
| performance_schema_max_memory_classes                    | 320   |
| performance_schema_max_metadata_locks                    | -1    |
| performance_schema_max_mutex_classes                     | 350   |
| performance_schema_max_mutex_instances                   | -1    |
| performance_schema_max_prepared_statements_instances     | -1    |
| performance_schema_max_program_instances                 | -1    |
| performance_schema_max_rwlock_classes                    | 40    |
| performance_schema_max_rwlock_instances                  | -1    |
| performance_schema_max_socket_classes                    | 10    |
| performance_schema_max_socket_instances                  | -1    |
| performance_schema_max_sql_text_length                   | 1024  |
| performance_schema_max_stage_classes                     | 150   |
| performance_schema_max_statement_classes                 | 192   |
| performance_schema_max_statement_stack                   | 10    |
| performance_schema_max_table_handles                     | -1    |
| performance_schema_max_table_instances                   | -1    |
| performance_schema_max_table_lock_stat                   | -1    |
| performance_schema_max_thread_classes                    | 50    |
| performance_schema_max_thread_instances                  | -1    |
| performance_schema_session_connect_attrs_size            | 512   |
| performance_schema_setup_actors_size                     | -1    |
| performance_schema_setup_objects_size                    | -1    |
| performance_schema_users_size                            | -1    |
+----------------------------------------------------------+-------+

Performance Schema system variables can be set at server startup on the command line or in option files, and many can be set at runtime. See Section 27.13, 鈥淧erformance Schema Option and Variable Reference鈥?/a>.

The Performance Schema automatically sizes the values of several of its parameters at server startup if they are not set explicitly. For more information, see Section 27.3, 鈥淧erformance Schema Startup Configuration鈥?/a>.

Performance Schema system variables have the following meanings:


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17.1.6.3 Replica Server Options and Variables

This section explains the server options and system variables that apply to replica servers and contains the following:

Specify the options either on the command line or in an option file. Many of the options can be set while the server is running by using the CHANGE REPLICATION SOURCE TO statement (from MySQL 8.0.23) or CHANGE MASTER TO statement (before MySQL 8.0.23). Specify system variable values using SET.

Server ID.  On the source and each replica, you must set the server_id system variable to establish a unique replication ID in the range from 1 to 232 鈭?1. 鈥?span class="quote">Unique鈥?/span> means that each ID must be different from every other ID in use by any other source or replica in the replication topology. Example my.cnf file:

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[mysqld] server-id=3
Startup Options for Replica Servers

This section explains startup options for controlling replica servers. Many of these options can be set while the server is running by using the CHANGE REPLICATION SOURCE TO statement (from MySQL 8.0.23) or CHANGE MASTER TO statement (before MySQL 8.0.23). Others, such as the --replicate-* options, can be set only when the replica server starts. Replication-related system variables are discussed later in this section.

The following options are used internally by the MySQL test suite for replication testing and debugging. They are not intended for use in a production setting.

  • --abort-slave-event-count

    Command-Line Format --abort-slave-event-count=#
    Deprecated 8.0.29
    Type Integer
    Default Value 0
    Minimum Value 0

    When this option is set to some positive integer value other than 0 (the default) it affects replication behavior as follows: After the replication SQL thread has started, value log events are permitted to be executed; after that, the replication SQL thread does not receive any more events, just as if the network connection from the source were cut. The replication SQL thread continues to run, and the output from SHOW REPLICA STATUS displays Yes in both the Replica_IO_Running and the Replica_SQL_Running columns, but no further events are read from the relay log.

    This option is used internally by the MySQL test suite for replication testing and debugging. It is not intended for use in a production setting. Beginning with MySQL 8.0.29, it is deprecated, and subject to removal in a future version of MySQL.

  • --disconnect-slave-event-count

    Command-Line Format --disconnect-slave-event-count=#
    Deprecated 8.0.29
    Type Integer
    Default Value 0

    This option is used internally by the MySQL test suite for replication testing and debugging. It is not intended for use in a production setting. Beginning with MySQL 8.0.29, it is deprecated, and subject to removal in a future version of MySQL.

System Variables Used on Replica Servers

The following list describes system variables for controlling replica servers. They can be set at server startup and some of them can be changed at runtime using SET. Server options used with replicas are listed earlier in this section.

  • init_replica

    Command-Line Format --init-replica=name
    Introduced 8.0.26
    System Variable init_replica
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type String

    From MySQL 8.0.26, use init_replica in place of init_slave, which is deprecated from that release. In releases before MySQL 8.0.26, use init_slave.

    init_replica is similar to init_connect, but is a string to be executed by a replica server each time the replication SQL thread starts. The format of the string is the same as for the init_connect variable. The setting of this variable takes effect for subsequent START REPLICA statements.

    Note

    The replication SQL thread sends an acknowledgment to the client before it executes init_replica. Therefore, it is not guaranteed that init_replica has been executed when START REPLICA returns. See Section 13.4.2.8, 鈥淪TART REPLICA Statement鈥?/a> for more information.

  • init_slave

    Command-Line Format --init-slave=name
    Deprecated 8.0.26
    System Variable init_slave
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type String

    From MySQL 8.0.26, init_slave is deprecated and the alias init_replica should be used instead. In releases before MySQL 8.0.26, use init_slave.

    init_slave is similar to init_connect, but is a string to be executed by a replica server each time the replication SQL thread starts. The format of the string is the same as for the init_connect variable. The setting of this variable takes effect for subsequent START REPLICA statements.

    Note

    The replication SQL thread sends an acknowledgment to the client before it executes init_slave. Therefore, it is not guaranteed that init_slave has been executed when START REPLICA returns. See Section 13.4.2.8, 鈥淪TART REPLICA Statement鈥?/a> for more information.

  • log_slow_replica_statements

    Command-Line Format --log-slow-replica-statements[={OFF|ON}]
    Introduced 8.0.26
    System Variable log_slow_replica_statements
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Boolean
    Default Value OFF

    From MySQL 8.0.26, use log_slow_replica_statements in place of log_slow_slave_statements, which is deprecated from that release. In releases before MySQL 8.0.26, use log_slow_slave_statements.

    When the slow query log is enabled, log_slow_replica_statements enables logging for queries that have taken more than long_query_time seconds to execute on the replica. Note that if row-based replication is in use (binlog_format=ROW), log_slow_replica_statements has no effect. Queries are only added to the replica's slow query log when they are logged in statement format in the binary log, that is, when binlog_format=STATEMENT is set, or when binlog_format=MIXED is set and the statement is logged in statement format. Slow queries that are logged in row format when binlog_format=MIXED is set, or that are logged when binlog_format=ROW is set, are not added to the replica's slow query log, even if log_slow_replica_statements is enabled.

    Setting log_slow_replica_statements has no immediate effect. The state of the variable applies on all subsequent START REPLICA statements. Also note that the global setting for long_query_time applies for the lifetime of the SQL thread. If you change that setting, you must stop and restart the replication SQL thread to implement the change there (for example, by issuing STOP REPLICA and START REPLICA statements with the SQL_THREAD option).

  • log_slow_slave_statements

    Command-Line Format --log-slow-slave-statements[={OFF|ON}]
    Deprecated 8.0.26
    System Variable log_slow_slave_statements
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Boolean
    Default Value OFF

    From MySQL 8.0.26, log_slow_slave_statements is deprecated and the alias log_slow_replica_statements should be used instead. In releases before MySQL 8.0.26, use log_slow_slave_statements.

    When the slow query log is enabled, log_slow_slave_statements enables logging for queries that have taken more than long_query_time seconds to execute on the replica. Note that if row-based replication is in use (binlog_format=ROW), log_slow_slave_statements has no effect. Queries are only added to the replica's slow query log when they are logged in statement format in the binary log, that is, when binlog_format=STATEMENT is set, or when binlog_format=MIXED is set and the statement is logged in statement format. Slow queries that are logged in row format when binlog_format=MIXED is set, or that are logged when binlog_format=ROW is set, are not added to the replica's slow query log, even if log_slow_slave_statements is enabled.

    Setting log_slow_slave_statements has no immediate effect. The state of the variable applies on all subsequent START REPLICA statements. Also note that the global setting for long_query_time applies for the lifetime of the SQL thread. If you change that setting, you must stop and restart the replication SQL thread to implement the change there (for example, by issuing STOP REPLICA and START REPLICA statements with the SQL_THREAD option).

  • master_info_repository

    Command-Line Format --master-info-repository={FILE|TABLE}
    Deprecated 8.0.23
    System Variable master_info_repository
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type String
    Default Value TABLE
    Valid Values

    FILE

    TABLE

    The use of this system variable is now deprecated. The setting TABLE is the default, and is required when multiple replication channels are configured. The alternative setting FILE was previously deprecated.

    With the default setting, the replica records metadata about the source, consisting of status and connection information, to an InnoDB table in the mysql system database named mysql.slave_master_info. For more information on the connection metadata repository, see Section 17.2.4, 鈥淩elay Log and Replication Metadata Repositories鈥?/a>.

    The FILE setting wrote the replica's connection metadata repository to a file, which was named master.info by default. The name could be changed using the --master-info-file option.

  • max_relay_log_size

    Command-Line Format --max-relay-log-size=#
    System Variable max_relay_log_size
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Integer
    Default Value 0
    Minimum Value 0
    Maximum Value 1073741824
    Unit bytes
    Block Size 4096

    If a write by a replica to its relay log causes the current log file size to exceed the value of this variable, the replica rotates the relay logs (closes the current file and opens the next one). If max_relay_log_size is 0, the server uses max_binlog_size for both the binary log and the relay log. If max_relay_log_size is greater than 0, it constrains the size of the relay log, which enables you to have different sizes for the two logs. You must set max_relay_log_size to between 4096 bytes and 1GB (inclusive), or to 0. The default value is 0. See Section 17.2.3, 鈥淩eplication Threads鈥?/a>.

  • relay_log

    Command-Line Format --relay-log=file_name
    System Variable relay_log
    Scope Global
    Dynamic No
    SET_VAR Hint Applies No
    Type File name

    The base name for relay log files. For the default replication channel, the default base name for relay logs is host_name-relay-bin. For non-default replication channels, the default base name for relay logs is host_name-relay-bin-channel, where channel is the name of the replication channel recorded in this relay log.

    The server writes the file in the data directory unless the base name is given with a leading absolute path name to specify a different directory. The server creates relay log files in sequence by adding a numeric suffix to the base name.

    The relay log and relay log index on a replication server cannot be given the same names as the binary log and binary log index, whose names are specified by the --log-bin and --log-bin-index options. The server issues an error message and does not start if the binary log and relay log file base names would be the same.

    Due to the manner in which MySQL parses server options, if you specify this variable at server startup, you must supply a value; the default base name is used only if the option is not actually specified. If you specify the relay_log system variable at server startup without specifying a value, unexpected behavior is likely to result; this behavior depends on the other options used, the order in which they are specified, and whether they are specified on the command line or in an option file. For more information about how MySQL handles server options, see Section 4.2.2, 鈥淪pecifying Program Options鈥?/a>.

    If you specify this variable, the value specified is also used as the base name for the relay log index file. You can override this behavior by specifying a different relay log index file base name using the relay_log_index system variable.

    When the server reads an entry from the index file, it checks whether the entry contains a relative path. If it does, the relative part of the path is replaced with the absolute path set using the relay_log system variable. An absolute path remains unchanged; in such a case, the index must be edited manually to enable the new path or paths to be used.

    You may find the relay_log system variable useful in performing the following tasks:

    • Creating relay logs whose names are independent of host names.

    • If you need to put the relay logs in some area other than the data directory because your relay logs tend to be very large and you do not want to decrease max_relay_log_size.

    • To increase speed by using load-balancing between disks.

    You can obtain the relay log file name (and path) from the relay_log_basename system variable.

  • relay_log_basename

    System Variable relay_log_basename
    Scope Global
    Dynamic No
    SET_VAR Hint Applies No
    Type File name
    Default Value datadir + '/' + hostname + '-relay-bin'

    Holds the base name and complete path to the relay log file. The maximum variable length is 256. This variable is set by the server and is read only.

  • relay_log_index

    Command-Line Format --relay-log-index=file_name
    System Variable relay_log_index
    Scope Global
    Dynamic No
    SET_VAR Hint Applies No
    Type File name
    Default Value *host_name*-relay-bin.index

    The name for the relay log index file. The maximum variable length is 256. If you do not specify this variable, but the relay_log system variable is specified, its value is used as the default base name for the relay log index file. If relay_log is also not specified, then for the default replication channel, the default name is host_name-relay-bin.index, using the name of the host machine. For non-default replication channels, the default name is host_name-relay-bin-channel.index, where channel is the name of the replication channel recorded in this relay log index.

    The default location for relay log files is the data directory, or any other location that was specified using the relay_log system variable. You can use the relay_log_index system variable to specify an alternative location, by adding a leading absolute path name to the base name to specify a different directory.

    The relay log and relay log index on a replication server cannot be given the same names as the binary log and binary log index, whose names are specified by the --log-bin and --log-bin-index options. The server issues an error message and does not start if the binary log and relay log file base names would be the same.

    Due to the manner in which MySQL parses server options, if you specify this variable at server startup, you must supply a value; the default base name is used only if the option is not actually specified. If you specify the relay_log_index system variable at server startup without specifying a value, unexpected behavior is likely to result; this behavior depends on the other options used, the order in which they are specified, and whether they are specified on the command line or in an option file. For more information about how MySQL handles server options, see Section 4.2.2, 鈥淪pecifying Program Options鈥?/a>.

  • relay_log_info_file

    Command-Line Format --relay-log-info-file=file_name
    Deprecated 8.0.18
    System Variable relay_log_info_file
    Scope Global
    Dynamic No
    SET_VAR Hint Applies No
    Type File name
    Default Value relay-log.info

    The use of this system variable is now deprecated. It was used to set the file name for the replica's applier metadata repository if relay_log_info_repository=FILE was set. relay_log_info_file and the use of the relay_log_info_repository system variable are deprecated because the use of a file for the applier metadata repository has been superseded by crash-safe tables. For information about the applier metadata repository, see Section 17.2.4.2, 鈥淩eplication Metadata Repositories鈥?/a>.

  • relay_log_info_repository

    Command-Line Format --relay-log-info-repository=value
    Deprecated 8.0.23
    System Variable relay_log_info_repository
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type String
    Default Value TABLE
    Valid Values

    FILE

    TABLE

    The use of this system variable is now deprecated. The setting TABLE is the default, and is required when multiple replication channels are configured. The TABLE setting for the replica's applier metadata repository is also required to make replication resilient to unexpected halts. See Section 17.4.2, 鈥淗andling an Unexpected Halt of a Replica鈥?/a> for more information. The alternative setting FILE was previously deprecated.

    With the default setting, the replica stores its applier metadata repository as an InnoDB table in the mysql system database named mysql.slave_relay_log_info. For more information on the applier metadata repository, see Section 17.2.4, 鈥淩elay Log and Replication Metadata Repositories鈥?/a>.

    The FILE setting wrote the replica's applier metadata repository to a file, which was named relay-log.info by default. The name could be changed using the relay_log_info_file system variable.

  • relay_log_purge

    Command-Line Format --relay-log-purge[={OFF|ON}]
    System Variable relay_log_purge
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Boolean
    Default Value ON

    Disables or enables automatic purging of relay log files as soon as they are not needed any more. The default value is 1 (ON).

  • relay_log_recovery

    Command-Line Format --relay-log-recovery[={OFF|ON}]
    System Variable relay_log_recovery
    Scope Global
    Dynamic No
    SET_VAR Hint Applies No
    Type Boolean
    Default Value OFF

    If enabled, this variable enables automatic relay log recovery immediately following server startup. The recovery process creates a new relay log file, initializes the SQL (applier) thread position to this new relay log, and initializes the I/O (receiver) thread to the applier thread position. Reading of the relay log from the source then continues. If SOURCE_AUTO_POSITION=1 was set for the replication channel using the CHANGE REPLICATION SOURCE TO option, the source position used to start replication might be the one received in the connection and not the ones assigned in this process.

    This global variable is read-only at runtime. Its value can be set with the --relay-log-recovery option at replica server startup, which should be used following an unexpected halt of a replica to ensure that no possibly corrupted relay logs are processed, and must be used in order to guarantee a crash-safe replica. The default value is 0 (disabled). For information on the combination of settings on a replica that is most resilient to unexpected halts, see Section 17.4.2, 鈥淗andling an Unexpected Halt of a Replica鈥?/a>.

    For a multithreaded replica (where replica_parallel_workers or slave_parallel_workers is greater than 0), setting --relay-log-recovery at startup automatically handles any inconsistencies and gaps in the sequence of transactions that have been executed from the relay log. These gaps can occur when file position based replication is in use. (For more details, see Section 17.5.1.34, 鈥淩eplication and Transaction Inconsistencies鈥?/a>.) The relay log recovery process deals with gaps using the same method as the START REPLICA UNTIL SQL_AFTER_MTS_GAPS statement would. When the replica reaches a consistent gap-free state, the relay log recovery process goes on to fetch further transactions from the source beginning at the SQL (applier) thread position. When GTID-based replication is in use, from MySQL 8.0.18 a multithreaded replica checks first whether MASTER_AUTO_POSITION is set to ON, and if it is, omits the step of calculating the transactions that should be skipped or not skipped, so that the old relay logs are not required for the recovery process.

    Note

    This variable does not affect the following Group Replication channels:

    • group_replication_applier

    • group_replication_recovery

    Any other channels running on a group are affected, such as a channel which is replicating from an outside source or another group.

  • relay_log_space_limit

    Command-Line Format --relay-log-space-limit=#
    System Variable relay_log_space_limit
    Scope Global
    Dynamic No
    SET_VAR Hint Applies No
    Type Integer
    Default Value 0
    Minimum Value 0
    Maximum Value 18446744073709551615
    Unit bytes

    The maximum amount of space to use for all relay logs.

  • replica_checkpoint_group

    Command-Line Format --replica-checkpoint-group=#
    Introduced 8.0.26
    System Variable replica_checkpoint_group
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Integer
    Default Value 512
    Minimum Value 32
    Maximum Value 524280
    Block Size 8

    From MySQL 8.0.26, use replica_checkpoint_group in place of slave_checkpoint_group, which is deprecated from that release. In releases before MySQL 8.0.26, use slave_checkpoint_group.

    replica_checkpoint_group sets the maximum number of transactions that can be processed by a multithreaded replica before a checkpoint operation is called to update its status as shown by SHOW REPLICA STATUS. Setting this variable has no effect on replicas for which multithreading is not enabled. Setting this variable has no immediate effect. The state of the variable applies on all subsequent START REPLICA commands.

    Note

    Multithreaded replicas are not currently supported by NDB Cluster, which silently ignores the setting for this variable. See Section 23.7.3, 鈥淜nown Issues in NDB Cluster Replication鈥?/a>, for more information.

    This variable works in combination with the replica_checkpoint_period system variable in such a way that, when either limit is exceeded, the checkpoint is executed and the counters tracking both the number of transactions and the time elapsed since the last checkpoint are reset.

    The minimum allowed value for this variable is 32, unless the server was built using -DWITH_DEBUG, in which case the minimum value is 1. The effective value is always a multiple of 8; you can set it to a value that is not such a multiple, but the server rounds it down to the next lower multiple of 8 before storing the value. (Exception: No such rounding is performed by the debug server.) Regardless of how the server was built, the default value is 512, and the maximum allowed value is 524280.

  • replica_checkpoint_period

    Command-Line Format --replica-checkpoint-period=#
    Introduced 8.0.26
    System Variable replica_checkpoint_period
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Integer
    Default Value 300
    Minimum Value 1
    Maximum Value 4294967295
    Unit milliseconds

    From MySQL 8.0.26, use replica_sql_verify_checksum in place of slave_sql_verify_checksum, which is deprecated from that release. In releases before MySQL 8.0.26, use slave_sql_verify_checksum.

    replica_checkpoint_period sets the maximum time (in milliseconds) that is allowed to pass before a checkpoint operation is called to update the status of a multithreaded replica as shown by SHOW REPLICA STATUS. Setting this variable has no effect on replicas for which multithreading is not enabled. Setting this variable takes effect for all replication channels immediately, including running channels.

    Note

    Multithreaded replicas are not currently supported by NDB Cluster, which silently ignores the setting for this variable. See Section 23.7.3, 鈥淜nown Issues in NDB Cluster Replication鈥?/a>, for more information.

    This variable works in combination with the replica_checkpoint_group system variable in such a way that, when either limit is exceeded, the checkpoint is executed and the counters tracking both the number of transactions and the time elapsed since the last checkpoint are reset.

    The minimum allowed value for this variable is 1, unless the server was built using -DWITH_DEBUG, in which case the minimum value is 0. Regardless of how the server was built, the default value is 300 milliseconds, and the maximum possible value is 4294967295 milliseconds (approximately 49.7 days).

  • replica_compressed_protocol

    Command-Line Format --replica-compressed-protocol[={OFF|ON}]
    Introduced 8.0.26
    System Variable replica_compressed_protocol
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Boolean
    Default Value OFF

    From MySQL 8.0.26, use replica_compressed_protocol in place of slave_compressed_protocol, which is deprecated. In releases before MySQL 8.0.26, use slave_compressed_protocol.

    replica_compressed_protocol specifies whether to use compression of the source/replica connection protocol if both source and replica support it. If this variable is disabled (the default), connections are uncompressed. Changes to this variable take effect on subsequent connection attempts; this includes after issuing a START REPLICA statement, as well as reconnections made by a running replication I/O (receiver) thread.

    Binary log transaction compression (available as of MySQL 8.0.20), which is activated by the binlog_transaction_compression system variable, can also be used to save bandwidth. If you use binary log transaction compression in combination with protocol compression, protocol compression has less opportunity to act on the data, but can still compress headers and those events and transaction payloads that are uncompressed. For more information on binary log transaction compression, see Section 5.4.4.5, 鈥淏inary Log Transaction Compression鈥?/a>.

    If replica_compressed_protocol is enabled, it takes precedence over any SOURCE_COMPRESSION_ALGORITHMS option specified for the CHANGE REPLICATION SOURCE TO statement. In this case, connections to the source use zlib compression if both the source and replica support that algorithm. If replica_compressed_protocol is disabled, the value of SOURCE_COMPRESSION_ALGORITHMS applies. For more information, see Section 4.2.8, 鈥淐onnection Compression Control鈥?/a>.

  • replica_exec_mode

    Command-Line Format --replica-exec-mode=mode
    Introduced 8.0.26
    System Variable replica_exec_mode
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Enumeration
    Default Value

    IDEMPOTENT (NDB)

    STRICT (Other)

    Valid Values

    STRICT

    IDEMPOTENT

    From MySQL 8.0.26, use replica_exec_mode in place of slave_exec_mode, which is deprecated from that release. In releases before MySQL 8.0.26, use slave_exec_mode.

    replica_exec_mode controls how a replication thread resolves conflicts and errors during replication. IDEMPOTENT mode causes suppression of duplicate-key and no-key-found errors; STRICT means no such suppression takes place.

    IDEMPOTENT mode is intended for use in multi-source replication, circular replication, and some other special replication scenarios for NDB Cluster Replication. (See Section 23.7.10, 鈥淣DB Cluster Replication: Bidirectional and Circular Replication鈥?/a>, and Section 23.7.11, 鈥淣DB Cluster Replication Conflict Resolution鈥?/a>, for more information.) NDB Cluster ignores any value explicitly set for replica_exec_mode, and always treats it as IDEMPOTENT.

    In MySQL Server 8.0, STRICT mode is the default value.

    Setting this variable takes immediate effect for all replication channels, including running channels.

    For storage engines other than NDB, IDEMPOTENT mode should be used only when you are absolutely sure that duplicate-key errors and key-not-found errors can safely be ignored. It is meant to be used in fail-over scenarios for NDB Cluster where multi-source replication or circular replication is employed, and is not recommended for use in other cases.

  • replica_load_tmpdir

    Command-Line Format --replica-load-tmpdir=dir_name
    Introduced 8.0.26
    System Variable replica_load_tmpdir
    Scope Global
    Dynamic No
    SET_VAR Hint Applies No
    Type Directory name
    Default Value Value of --tmpdir

    From MySQL 8.0.26, use replica_load_tmpdir in place of slave_load_tmpdir, which is deprecated from that release. In releases before MySQL 8.0.26, use slave_load_tmpdir.

    replica_load_tmpdir specifies the name of the directory where the replica creates temporary files. Setting this variable takes effect for all replication channels immediately, including running channels. The variable value is by default equal to the value of the tmpdir system variable, or the default that applies when that system variable is not specified.

    When the replication SQL thread replicates a LOAD DATA statement, it extracts the file to be loaded from the relay log into temporary files, and then loads these into the table. If the file loaded on the source is huge, the temporary files on the replica are huge, too. Therefore, it might be advisable to use this option to tell the replica to put temporary files in a directory located in some file system that has a lot of available space. In that case, the relay logs are huge as well, so you might also want to set the relay_log system variable to place the relay logs in that file system.

    The directory specified by this option should be located in a disk-based file system (not a memory-based file system) so that the temporary files used to replicate LOAD DATA statements can survive machine restarts. The directory also should not be one that is cleared by the operating system during the system startup process. However, replication can now continue after a restart if the temporary files have been removed.

  • replica_max_allowed_packet

    Command-Line Format --replica-max-allowed-packet=#
    Introduced 8.0.26
    System Variable replica_max_allowed_packet
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Integer
    Default Value 1073741824
    Minimum Value 1024
    Maximum Value 1073741824
    Unit bytes
    Block Size 1024

    From MySQL 8.0.26, use replica_max_allowed_packet in place of slave_max_allowed_packet, which is deprecated from that release. In releases before MySQL 8.0.26, use slave_max_allowed_packet.

    replica_max_allowed_packet sets the maximum packet size in bytes that the replication SQL (applier)and I/O (receiver) threads can handle. Setting this variable takes effect for all replication channels immediately, including running channels. It is possible for a source to write binary log events longer than its max_allowed_packet setting once the event header is added. The setting for replica_max_allowed_packet must be larger than the max_allowed_packet setting on the source, so that large updates using row-based replication do not cause replication to fail.

    This global variable always has a value that is a positive integer multiple of 1024; if you set it to some value that is not, the value is rounded down to the next highest multiple of 1024 for it is stored or used; setting replica_max_allowed_packet to 0 causes 1024 to be used. (A truncation warning is issued in all such cases.) The default and maximum value is 1073741824 (1 GB); the minimum is 1024.

  • replica_net_timeout

    Command-Line Format --replica-net-timeout=#
    Introduced 8.0.26
    System Variable replica_net_timeout
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Integer
    Default Value 60
    Minimum Value 1
    Maximum Value 31536000
    Unit seconds

    From MySQL 8.0.26, use replica_net_timeout in place of slave_net_timeout, which is deprecated from that release. In releases before MySQL 8.0.26, use slave_net_timeout.

    replica_net_timeout specifies the number of seconds to wait for more data or a heartbeat signal from the source before the replica considers the connection broken, aborts the read, and tries to reconnect. Setting this variable has no immediate effect. The state of the variable applies on all subsequent START REPLICA commands.

    The default value is 60 seconds (one minute). The first retry occurs immediately after the timeout. The interval between retries is controlled by the SOURCE_CONNECT_RETRY option for the CHANGE REPLICATION SOURCE TO statement, and the number of reconnection attempts is limited by the SOURCE_RETRY_COUNT option.

    The heartbeat interval, which stops the connection timeout occurring in the absence of data if the connection is still good, is controlled by the SOURCE_HEARTBEAT_PERIOD option for the CHANGE REPLICATION SOURCE TO statement. The heartbeat interval defaults to half the value of replica_net_timeout, and it is recorded in the replica's connection metadata repository and shown in the replication_connection_configuration Performance Schema table. Note that a change to the value or default setting of replica_net_timeout does not automatically change the heartbeat interval, whether that has been set explicitly or is using a previously calculated default. If the connection timeout is changed, you must also issue CHANGE REPLICATION SOURCE TO to adjust the heartbeat interval to an appropriate value so that it occurs before the connection timeout.

  • replica_parallel_type

    Command-Line Format --replica-parallel-type=value
    Introduced 8.0.26
    Deprecated 8.0.29
    System Variable replica_parallel_type
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Enumeration
    Default Value (鈮?8.0.27) LOGICAL_CLOCK
    Default Value (8.0.26) DATABASE
    Valid Values

    DATABASE

    LOGICAL_CLOCK

    From MySQL 8.0.26, use replica_parallel_type in place of slave_parallel_type, which is deprecated from that release. In releases before MySQL 8.0.26, use slave_parallel_type.

    For multithreaded replicas (replicas on which replica_parallel_workers or slave_parallel_workers is set to a value greater than 0), replica_parallel_type specifies the policy used to decide which transactions are allowed to execute in parallel on the replica. The variable has no effect on replicas for which multithreading is not enabled. The possible values are:

    • LOGICAL_CLOCK: Transactions are applied in parallel on the replica, based on timestamps which the replication source writes to the binary log. Dependencies between transactions are tracked based on their timestamps to provide additional parallelization where possible.

    • DATABASE: Transactions that update different databases are applied in parallel. This value is only appropriate if data is partitioned into multiple databases which are being updated independently and concurrently on the source. There must be no cross-database constraints, as such constraints may be violated on the replica.

    When replica_preserve_commit_order or slave_preserve_commit_order is enabled, you must use LOGICAL_CLOCK. Before MySQL 8.0.27, DATABASE is the default. From MySQL 8.0.27, multithreading is enabled by default for replica servers (replica_parallel_workers=4 by default), and LOGICAL_CLOCK is the default. (In MySQL 8.0.27 and later, replica_preserve_commit_order is also enabled by default.)

    When the replication topology uses multiple levels of replicas, LOGICAL_CLOCK may achieve less parallelization for each level the replica is away from the source. To compensate for this effect, you should set binlog_transaction_dependency_tracking to WRITESET or WRITESET_SESSION on the source as well as on every intermediate replica to specify that write sets are used instead of timestamps for parallelization where possible.

    When binary log transaction compression is enabled using the binlog_transaction_compression system variable, if replica_parallel_type is set to DATABASE, all the databases affected by the transaction are mapped before the transaction is scheduled. The use of binary log transaction compression with the DATABASE policy can reduce parallelism compared to uncompressed transactions, which are mapped and scheduled for each event.

    replica_parallel_type is deprecated beginning with MySQL 8.0.29, as is support for parallelization of transactions using database partitioning. Expect support for these to be removed in a future release, and for LOGICAL_CLOCK to be used exclusively thereafter.

  • replica_parallel_workers

    Command-Line Format --replica-parallel-workers=#
    Introduced 8.0.26
    System Variable replica_parallel_workers
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Integer
    Default Value (鈮?8.0.27) 4
    Default Value (8.0.26) 0
    Minimum Value 0
    Maximum Value 1024

    From MySQL 8.0.26, use replica_parallel_workers in place of slave_parallel_workers, which is deprecated from that release. In releases before MySQL 8.0.26, use slave_parallel_workers.

    replica_parallel_workers enables multithreading on the replica and sets the number of applier threads for executing replication transactions in parallel. When the value is a number greater than 1, the replica is a multithreaded replica with the specified number of applier threads, plus a coordinator thread to manage them. If you are using multiple replication channels, each channel has this number of threads.

    Before MySQL 8.0.27, the default for this system variable is 0, so replicas are single-threaded by default. From MySQL 8.0.27, the default is 4, so replicas are multithreaded by default.

    Beginning with MySQL 8.0.30, setting this variable to 0 is deprecated, and doing so raises a warning; 0 as a permitted value for replica_parallel_workers is subject to removal in a future MySQL release; set it to 1 instead, which has the same effect.

    Retrying of transactions is supported when multithreading is enabled on a replica. When replica_preserve_commit_order=ON or slave_preserve_commit_order=ON is set, transactions on a replica are externalized on the replica in the same order as they appear in the replica's relay log. The way in which transactions are distributed among applier threads is configured by replica_parallel_type (from MySQL 8.0.26) or slave_parallel_type (before MySQL 8.0.26). From MySQL 8.0.27, these system variables also have appropriate defaults for multithreading.

    To disable parallel execution, set replica_parallel_workers to 1, which gives the replica a single applier thread and no coordinator thread. With this setting, the replica_parallel_type or slave_parallel_type and replica_preserve_commit_order or slave_preserve_commit_order system variables have no effect and are ignored. From MySQL 8.0.27, if parallel execution is disabled when the CHANGE REPLICATION SOURCE TO option GTID_ONLY is enabled on a replica, the replica actually uses one parallel worker to take advantage of the method for retrying transactions without accessing the file positions. With one parallel worker, the replica_preserve_commit_order or slave_preserve_commit_order system variable also has no effect.

    Setting replica_parallel_workers has no immediate effect. The state of the variable applies on all subsequent START REPLICA statements.

    Note

    Multithreaded replicas are not currently supported by NDB Cluster. See Section 23.7.3, 鈥淜nown Issues in NDB Cluster Replication鈥?/a>, for more information about how NDB handles settings for this variable.

  • replica_pending_jobs_size_max

    Command-Line Format --replica-pending-jobs-size-max=#
    Introduced 8.0.26
    System Variable replica_pending_jobs_size_max
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Integer
    Default Value 128M
    Minimum Value 1024
    Maximum Value 16EiB
    Unit bytes
    Block Size 1024

    From MySQL 8.0.26, use replica_pending_jobs_size_max in place of slave_pending_jobs_size_max, which is deprecated from that release. In releases before MySQL 8.0.26, use slave_pending_jobs_size_max.

    For multithreaded replicas, this variable sets the maximum amount of memory (in bytes) available to applier queues holding events not yet applied. Setting this variable has no effect on replicas for which multithreading is not enabled. Setting this variable has no immediate effect. The state of the variable applies on all subsequent START REPLICA commands.

    The minimum possible value for this variable is 1024 bytes; the default is 128MB. The maximum possible value is 18446744073709551615 (16 exbibytes). Values that are not exact multiples of 1024 bytes are rounded down to the next lower multiple of 1024 bytes prior to being stored.

    The value of this variable is a soft limit and can be set to match the normal workload. If an unusually large event exceeds this size, the transaction is held until all the worker threads have empty queues, and then processed. All subsequent transactions are held until the large transaction has been completed.

  • replica_preserve_commit_order

    Command-Line Format --replica-preserve-commit-order[={OFF|ON}]
    Introduced 8.0.26
    System Variable replica_preserve_commit_order
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Boolean
    Default Value (鈮?8.0.27) ON
    Default Value (8.0.26) OFF

    From MySQL 8.0.26, use replica_preserve_commit_order in place of slave_preserve_commit_order, which is deprecated from that release. In releases before MySQL 8.0.26, use slave_preserve_commit_order.

    For multithreaded replicas (replicas on which replica_parallel_workers is set to a value greater than 0), setting replica_preserve_commit_order=ON ensures that transactions are executed and committed on the replica in the same order as they appear in the replica's relay log. This prevents gaps in the sequence of transactions that have been executed from the replica's relay log, and preserves the same transaction history on the replica as on the source (with the limitations listed below). This variable has no effect on replicas for which multithreading is not enabled.

    Before MySQL 8.0.27, the default for this system variable is OFF, meaning that transactions may be committed out of order. From MySQL 8.0.27, multithreading is enabled by default for replica servers (replica_parallel_workers=4 by default), so replica_preserve_commit_order=ON is the default, and the setting replica_parallel_type=LOGICAL_CLOCK is also the default. Also from MySQL 8.0.27, the setting for replica_preserve_commit_order is ignored if replica_parallel_workers is set to 1, because in that situation the order of transactions is preserved anyway.

    Binary logging and replica update logging are not required on the replica to set replica_preserve_commit_order=ON, and can be disabled if wanted. Setting replica_preserve_commit_order=ON requires that replica_parallel_type is set to LOGICAL_CLOCK, which is not the default setting before MySQL 8.0.27. Before changing the value of replica_preserve_commit_order and replica_parallel_type, the replication SQL thread (for all replication channels if you are using multiple replication channels) must be stopped.

    When replica_preserve_commit_order=OFF is set, the transactions that a multithreaded replica applies in parallel may commit out of order. Therefore, checking for the most recently executed transaction does not guarantee that all previous transactions from the source have been executed on the replica. There is a chance of gaps in the sequence of transactions that have been executed from the replica's relay log. This has implications for logging and recovery when using a multithreaded replica. See Section 17.5.1.34, 鈥淩eplication and Transaction Inconsistencies鈥?/a> for more information.

    When replica_preserve_commit_order=ON is set, the executing worker thread waits until all previous transactions are committed before committing. While a given thread is waiting for other worker threads to commit their transactions, it reports its status as Waiting for preceding transaction to commit. With this mode, a multithreaded replica never enters a state that the source was not in. This supports the use of replication for read scale-out. See Section 17.4.5, 鈥淯sing Replication for Scale-Out鈥?/a>.

    Note
    • replica_preserve_commit_order=ON does not prevent source binary log position lag, where Exec_master_log_pos is behind the position up to which transactions have been executed. See Section 17.5.1.34, 鈥淩eplication and Transaction Inconsistencies鈥?/a>.

    • replica_preserve_commit_order=ON does not preserve the commit order and transaction history if the replica uses filters on its binary log, such as --binlog-do-db.

    • replica_preserve_commit_order=ON does not preserve the order of non-transactional DML updates. These might commit before transactions that precede them in the relay log, which might result in gaps in the sequence of transactions that have been executed from the replica's relay log.

    • A limitation to preserving the commit order on the replica can occur if statement-based replication is in use, and both transactional and non-transactional storage engines participate in a non-XA transaction that is rolled back on the source. Normally, non-XA transactions that are rolled back on the source are not replicated to the replica, but in this particular situation, the transaction might be replicated to the replica. If this does happen, a multithreaded replica without binary logging does not handle the transaction rollback, so the commit order on the replica diverges from the relay log order of the transactions in that case.

  • replica_sql_verify_checksum

    Command-Line Format --replica-sql-verify-checksum[={OFF|ON}]
    Introduced 8.0.26
    System Variable replica_sql_verify_checksum
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Boolean
    Default Value ON

    From MySQL 8.0.26, use replica_sql_verify_checksum in place of slave_sql_verify_checksum, which is deprecated from that release. In releases before MySQL 8.0.26, use slave_sql_verify_checksum.

    slave_sql_verify_checksum causes the replication SQL (applier) thread to verify data using the checksums read from the relay log. In the event of a mismatch, the replica stops with an error. Setting this variable takes effect for all replication channels immediately, including running channels.

    Note

    The replication I/O (receiver)thread always reads checksums if possible when accepting events from over the network.

  • replica_transaction_retries

    Command-Line Format --replica-transaction-retries=#
    Introduced 8.0.26
    System Variable replica_transaction_retries
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Integer
    Default Value 10
    Minimum Value 0
    Maximum Value 18446744073709551615

    From MySQL 8.0.26, use replica_transaction_retries in place of slave_transaction_retries, which is deprecated from that release. In releases before MySQL 8.0.26, use slave_transaction_retries.

    replica_transaction_retries sets the maximum number of times for replication SQL threads on a single-threaded or multithreaded replica to automatically retry failed transactions before stopping. Setting this variable takes effect for all replication channels immediately, including running channels. The default value is 10. Setting the variable to 0 disables automatic retrying of transactions.

    If a replication SQL thread fails to execute a transaction because of an InnoDB deadlock or because the transaction's execution time exceeded InnoDB's innodb_lock_wait_timeout or NDB's TransactionDeadlockDetectionTimeout or TransactionInactiveTimeout, it automatically retries replica_transaction_retries times before stopping with an error. Transactions with a non-temporary error are not retried.

    The Performance Schema table replication_applier_status shows the number of retries that took place on each replication channel, in the COUNT_TRANSACTIONS_RETRIES column. The Performance Schema table replication_applier_status_by_worker shows detailed information on transaction retries by individual applier threads on a single-threaded or multithreaded replica, and identifies the errors that caused the last transaction and the transaction currently in progress to be reattempted.

  • replica_type_conversions

    Command-Line Format --replica-type-conversions=set
    Introduced 8.0.26
    System Variable replica_type_conversions
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Set
    Default Value
    Valid Values

    ALL_LOSSY

    ALL_NON_LOSSY

    ALL_SIGNED

    ALL_UNSIGNED

    From MySQL 8.0.26, use replica_type_conversions in place of slave_type_conversions, which is deprecated from that release. In releases before MySQL 8.0.26, use slave_type_conversions.

    replica_type_conversions controls the type conversion mode in effect on the replica when using row-based replication. Its value is a comma-delimited set of zero or more elements from the list: ALL_LOSSY, ALL_NON_LOSSY, ALL_SIGNED, ALL_UNSIGNED. Set this variable to an empty string to disallow type conversions between the source and the replica. Setting this variable takes effect for all replication channels immediately, including running channels.

    For additional information on type conversion modes applicable to attribute promotion and demotion in row-based replication, see Row-based replication: attribute promotion and demotion.

  • replication_optimize_for_static_plugin_config

    Command-Line Format --replication-optimize-for-static-plugin-config[={OFF|ON}]
    Introduced 8.0.23
    System Variable replication_optimize_for_static_plugin_config
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Boolean
    Default Value OFF

    Use shared locks, and avoid unnecessary lock acquisitions, to improve performance for semisynchronous replication. This setting and replication_sender_observe_commit_only help as the number of replicas increases, because contention for locks can slow down performance. While this system variable is enabled, the semisynchronous replication plugin cannot be uninstalled, so you must disable the system variable before the uninstall can complete.

    This system variable can be enabled before or after installing the semisynchronous replication plugin, and can be enabled while replication is running. Semisynchronous replication source servers can also get performance benefits from enabling this system variable, because they use the same locking mechanisms as the replicas.

    replication_optimize_for_static_plugin_config can be enabled when Group Replication is in use on a server. In that scenario, it might benefit performance when there is contention for locks due to high workloads.

  • replication_sender_observe_commit_only

    Command-Line Format --replication-sender-observe-commit-only[={OFF|ON}]
    Introduced 8.0.23
    System Variable replication_sender_observe_commit_only
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Boolean
    Default Value OFF

    Limit callbacks to improve performance for semisynchronous replication. This setting and replication_optimize_for_static_plugin_config help as the number of replicas increases, because contention for locks can slow down performance.

    This system variable can be enabled before or after installing the semisynchronous replication plugin, and can be enabled while replication is running. Semisynchronous replication source servers can also get performance benefits from enabling this system variable, because they use the same locking mechanisms as the replicas.

  • report_host

    Command-Line Format --report-host=host_name
    System Variable report_host
    Scope Global
    Dynamic No
    SET_VAR Hint Applies No
    Type String

    The host name or IP address of the replica to be reported to the source during replica registration. This value appears in the output of SHOW REPLICAS on the source server. Leave the value unset if you do not want the replica to register itself with the source.

    Note

    It is not sufficient for the source to simply read the IP address of the replica server from the TCP/IP socket after the replica connects. Due to NAT and other routing issues, that IP may not be valid for connecting to the replica from the source or other hosts.

  • report_password

    Command-Line Format --report-password=name
    System Variable report_password
    Scope Global
    Dynamic No
    SET_VAR Hint Applies No
    Type String

    The account password of the replica to be reported to the source during replica registration. This value appears in the output of SHOW REPLICAS on the source server if the source was started with --show-replica-auth-info or --show-slave-auth-info.

    Although the name of this variable might imply otherwise, report_password is not connected to the MySQL user privilege system and so is not necessarily (or even likely to be) the same as the password for the MySQL replication user account.

  • report_port

    Command-Line Format --report-port=port_num
    System Variable report_port
    Scope Global
    Dynamic No
    SET_VAR Hint Applies No
    Type Integer
    Default Value [slave_port]
    Minimum Value 0
    Maximum Value 65535

    The TCP/IP port number for connecting to the replica, to be reported to the source during replica registration. Set this only if the replica is listening on a nondefault port or if you have a special tunnel from the source or other clients to the replica. If you are not sure, do not use this option.

    The default value for this option is the port number actually used by the replica. This is also the default value displayed by SHOW REPLICAS.

  • report_user

    Command-Line Format --report-user=name
    System Variable report_user
    Scope Global
    Dynamic No
    SET_VAR Hint Applies No
    Type String

    The account user name of the replica to be reported to the source during replica registration. This value appears in the output of SHOW REPLICAS on the source server if the source was started with --show-replica-auth-info or --show-slave-auth-info.

    Although the name of this variable might imply otherwise, report_user is not connected to the MySQL user privilege system and so is not necessarily (or even likely to be) the same as the name of the MySQL replication user account.

  • rpl_read_size

    Command-Line Format --rpl-read-size=#
    System Variable rpl_read_size
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Integer
    Default Value 8192
    Minimum Value 8192
    Maximum Value 4294959104
    Unit bytes
    Block Size 8192

    The rpl_read_size system variable controls the minimum amount of data in bytes that is read from the binary log files and relay log files. If heavy disk I/O activity for these files is impeding performance for the database, increasing the read size might reduce file reads and I/O stalls when the file data is not currently cached by the operating system.

    The minimum and default value for rpl_read_size is 8192 bytes. The value must be a multiple of 4KB. Note that a buffer the size of this value is allocated for each thread that reads from the binary log and relay log files, including dump threads on sources and coordinator threads on replicas. Setting a large value might therefore have an impact on memory consumption for servers.

  • rpl_semi_sync_replica_enabled

    Command-Line Format --rpl-semi-sync-replica-enabled[={OFF|ON}]
    Introduced 8.0.26
    System Variable rpl_semi_sync_replica_enabled
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Boolean
    Default Value OFF

    rpl_semi_sync_replica_enabled is available when the rpl_semi_sync_replica (semisync_replica.so library) plugin was installed on the replica to set up semisynchronous replication. If the rpl_semi_sync_slave plugin (semisync_slave.so library) was installed, rpl_semi_sync_slave_enabled is available instead.

    rpl_semi_sync_replica_enabled controls whether semisynchronous replication is enabled on the replica server. To enable or disable the plugin, set this variable to ON or OFF (or 1 or 0), respectively. The default is OFF.

    This variable is available only if the replica-side semisynchronous replication plugin is installed.

  • rpl_semi_sync_replica_trace_level

    Command-Line Format --rpl-semi-sync-replica-trace-level=#
    Introduced 8.0.26
    System Variable rpl_semi_sync_replica_trace_level
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Integer
    Default Value 32
    Minimum Value 0
    Maximum Value 4294967295

    rpl_semi_sync_replica_trace_level is available when the rpl_semi_sync_replica (semisync_replica.so library) plugin was installed on the replica to set up semisynchronous replication. If the rpl_semi_sync_slave plugin (semisync_slave.so library) was installed, rpl_semi_sync_slave_trace_level is available instead.

    rpl_semi_sync_replica_trace_level controls the semisynchronous replication debug trace level on the replica server. See rpl_semi_sync_master_trace_level for the permissible values.

    This variable is available only if the replica-side semisynchronous replication plugin is installed.

  • rpl_semi_sync_slave_enabled

    Command-Line Format --rpl-semi-sync-slave-enabled[={OFF|ON}]
    System Variable rpl_semi_sync_slave_enabled
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Boolean
    Default Value OFF

    rpl_semi_sync_slave_enabled is available when the rpl_semi_sync_slave (semisync_slave.so library) plugin was installed on the replica to set up semisynchronous replication. If the rpl_semi_sync_replica plugin (semisync_replica.so library) was installed, rpl_semi_sync_replica_enabled is available instead.

    rpl_semi_sync_slave_enabled controls whether semisynchronous replication is enabled on the replica server. To enable or disable the plugin, set this variable to ON or OFF (or 1 or 0), respectively. The default is OFF.

    This variable is available only if the replica-side semisynchronous replication plugin is installed.

  • rpl_semi_sync_slave_trace_level

    Command-Line Format --rpl-semi-sync-slave-trace-level=#
    System Variable rpl_semi_sync_slave_trace_level
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Integer
    Default Value 32
    Minimum Value 0
    Maximum Value 4294967295

    rpl_semi_sync_slave_trace_level is available when the rpl_semi_sync_slave (semisync_slave.so library) plugin was installed on the replica to set up semisynchronous replication. If the rpl_semi_sync_replica plugin (semisync_replica.so library) was installed, rpl_semi_sync_replica_trace_level is available instead.

    rpl_semi_sync_slave_trace_level controls the semisynchronous replication debug trace level on the replica server. See rpl_semi_sync_master_trace_level for the permissible values.

    This variable is available only if the replica-side semisynchronous replication plugin is installed.

  • rpl_stop_replica_timeout

    Command-Line Format --rpl-stop-replica-timeout=#
    Introduced 8.0.26
    System Variable rpl_stop_replica_timeout
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Integer
    Default Value 31536000
    Minimum Value 2
    Maximum Value 31536000
    Unit seconds

    From MySQL 8.0.26, use rpl_stop_replica_timeout in place of rpl_stop_slave_timeout, which is deprecated from that release. In releases before MySQL 8.0.26, use rpl_stop_slave_timeout.

    You can control the length of time (in seconds) that STOP REPLICA waits before timing out by setting this variable. This can be used to avoid deadlocks between STOP REPLICA and other SQL statements using different client connections to the replica.

    The maximum and default value of rpl_stop_replica_timeout is 31536000 seconds (1 year). The minimum is 2 seconds. Changes to this variable take effect for subsequent STOP REPLICA statements.

    This variable affects only the client that issues a STOP REPLICA statement. When the timeout is reached, the issuing client returns an error message stating that the command execution is incomplete. The client then stops waiting for the replication I/O (receiver)and SQL (applier) threads to stop, but the replication threads continue to try to stop, and the STOP REPLICA instruction remains in effect. Once the replication threads are no longer busy, the STOP REPLICA statement is executed and the replica stops.

  • rpl_stop_slave_timeout

    Command-Line Format --rpl-stop-slave-timeout=#
    Deprecated 8.0.26
    System Variable rpl_stop_slave_timeout
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Integer
    Default Value 31536000
    Minimum Value 2
    Maximum Value 31536000
    Unit seconds

    From MySQL 8.0.26, rpl_stop_slave_timeout is deprecated and the alias rpl_stop_replica_timeout should be used instead. In releases before MySQL 8.0.26, use rpl_stop_slave_timeout.

    You can control the length of time (in seconds) that STOP REPLICA waits before timing out by setting this variable. This can be used to avoid deadlocks between STOP REPLICA and other SQL statements using different client connections to the replica.

    The maximum and default value of rpl_stop_slave_timeout is 31536000 seconds (1 year). The minimum is 2 seconds. Changes to this variable take effect for subsequent STOP REPLICA statements.

    This variable affects only the client that issues a STOP REPLICA statement. When the timeout is reached, the issuing client returns an error message stating that the command execution is incomplete. The client then stops waiting for the replication I/O (receiver) and SQL (applier) threads to stop, but the replication threads continue to try to stop, and the STOP REPLICA instruction remains in effect. Once the replication threads are no longer busy, the STOP REPLICA statement is executed and the replica stops.

  • skip_replica_start

    Command-Line Format --skip-replica-start[={OFF|ON}]
    Introduced 8.0.26
    System Variable skip_replica_start
    Scope Global
    Dynamic No
    SET_VAR Hint Applies No
    Type Boolean
    Default Value OFF

    From MySQL 8.0.26, use skip_replica_start in place of skip_slave_start, which is deprecated from that release. In releases before MySQL 8.0.26, use skip_slave_start.

    skip_replica_start tells the replica server not to start the replication I/O (receiver) and SQL (applier) threads when the server starts. To start the threads later, use a START REPLICA statement.

    This system variable is read-only and can be set by using the PERSIST_ONLY keyword or the @@persist_only qualifier with the SET statement. The --skip-replica-start command line option also sets this system variable. You can use the system variable in place of the command line option to allow access to this feature using MySQL Server鈥檚 privilege structure, so that database administrators do not need any privileged access to the operating system.

  • skip_slave_start

    Command-Line Format --skip-slave-start[={OFF|ON}]
    Deprecated 8.0.26
    System Variable skip_slave_start
    Scope Global
    Dynamic No
    SET_VAR Hint Applies No
    Type Boolean
    Default Value OFF

    From MySQL 8.0.26, skip_slave_start is deprecated and the alias skip_replica_start should be used instead. In releases before MySQL 8.0.26, use skip_slave_start.

    Tells the replica server not to start the replication I/O (receiver) and SQL (applier) threads when the server starts. To start the threads later, use a START REPLICA statement.

    This system variable is available from MySQL 8.0.24. It is read-only and can be set by using the PERSIST_ONLY keyword or the @@persist_only qualifier with the SET statement. The --skip-slave-start command line option also sets this system variable. You can use the system variable in place of the command line option to allow access to this feature using MySQL Server鈥檚 privilege structure, so that database administrators do not need any privileged access to the operating system.

  • slave_checkpoint_group

    Command-Line Format --slave-checkpoint-group=#
    Deprecated 8.0.26
    System Variable slave_checkpoint_group
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Integer
    Default Value 512
    Minimum Value 32
    Maximum Value 524280
    Block Size 8

    From MySQL 8.0.26, slave_checkpoint_group is deprecated and the alias replica_checkpoint_group should be used instead. In releases before MySQL 8.0.26, use slave_checkpoint_group.

    slave_checkpoint_group sets the maximum number of transactions that can be processed by a multithreaded replica before a checkpoint operation is called to update its status as shown by SHOW REPLICA STATUS. Setting this variable has no effect on replicas for which multithreading is not enabled. Setting this variable has no immediate effect. The state of the variable applies on all subsequent START REPLICA commands.

    Note

    Multithreaded replicas are not currently supported by NDB Cluster, which silently ignores the setting for this variable. See Section 23.7.3, 鈥淜nown Issues in NDB Cluster Replication鈥?/a>, for more information.

    This variable works in combination with the slave_checkpoint_period system variable in such a way that, when either limit is exceeded, the checkpoint is executed and the counters tracking both the number of transactions and the time elapsed since the last checkpoint are reset.

    The minimum allowed value for this variable is 32, unless the server was built using -DWITH_DEBUG, in which case the minimum value is 1. The effective value is always a multiple of 8; you can set it to a value that is not such a multiple, but the server rounds it down to the next lower multiple of 8 before storing the value. (Exception: No such rounding is performed by the debug server.) Regardless of how the server was built, the default value is 512, and the maximum allowed value is 524280.

  • slave_checkpoint_period

    Command-Line Format --slave-checkpoint-period=#
    Deprecated 8.0.26
    System Variable slave_checkpoint_period
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Integer
    Default Value 300
    Minimum Value 1
    Maximum Value 4294967295
    Unit milliseconds

    From MySQL 8.0.26, slave_checkpoint_period is deprecated and the alias replica_checkpoint_period should be used instead. In releases before MySQL 8.0.26, use slave_checkpoint_period.

    slave_checkpoint_period sets the maximum time (in milliseconds) that is allowed to pass before a checkpoint operation is called to update the status of a multithreaded replica as shown by SHOW REPLICA STATUS. Setting this variable has no effect on replicas for which multithreading is not enabled. Setting this variable takes effect for all replication channels immediately, including running channels.

    Note

    Multithreaded replicas are not currently supported by NDB Cluster, which silently ignores the setting for this variable. See Section 23.7.3, 鈥淜nown Issues in NDB Cluster Replication鈥?/a>, for more information.

    This variable works in combination with the slave_checkpoint_group system variable in such a way that, when either limit is exceeded, the checkpoint is executed and the counters tracking both the number of transactions and the time elapsed since the last checkpoint are reset.

    The minimum allowed value for this variable is 1, unless the server was built using -DWITH_DEBUG, in which case the minimum value is 0. Regardless of how the server was built, the default value is 300 milliseconds, and the maximum possible value is 4294967295 milliseconds (approximately 49.7 days).

  • slave_compressed_protocol

    Command-Line Format --slave-compressed-protocol[={OFF|ON}]
    Deprecated 8.0.18
    System Variable slave_compressed_protocol
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Boolean
    Default Value OFF

    slave_compressed_protocol is deprecated, and from MySQL 8.0.26, the alias replica_compressed_protocol should be used instead. In releases before MySQL 8.0.26, use slave_compressed_protocol.

    slave_compressed_protocol controls whether to use compression of the source/replica connection protocol if both source and replica support it. If this variable is disabled (the default), connections are uncompressed. Changes to this variable take effect on subsequent connection attempts; this includes after issuing a START REPLICA statement, as well as reconnections made by a running replication I/O (receiver) thread.

    Binary log transaction compression (available as of MySQL 8.0.20), which is activated by the binlog_transaction_compression system variable, can also be used to save bandwidth. If you use binary log transaction compression in combination with protocol compression, protocol compression has less opportunity to act on the data, but can still compress headers and those events and transaction payloads that are uncompressed. For more information on binary log transaction compression, see Section 5.4.4.5, 鈥淏inary Log Transaction Compression鈥?/a>.

    As of MySQL 8.0.18, if slave_compressed_protocol is enabled, it takes precedence over any SOURCE_COMPRESSION_ALGORITHMS | MASTER_COMPRESSION_ALGORITHMS option specified for the CHANGE REPLICATION SOURCE TO | CHANGE MASTER TO statement. In this case, connections to the source use zlib compression if both the source and replica support that algorithm. If slave_compressed_protocol is disabled, the value of SOURCE_COMPRESSION_ALGORITHMS | MASTER_COMPRESSION_ALGORITHMS applies. For more information, see Section 4.2.8, 鈥淐onnection Compression Control鈥?/a>.

    As of MySQL 8.0.18, this system variable is deprecated. You should expect it to be removed in a future version of MySQL. See Configuring Legacy Connection Compression.

  • slave_exec_mode

    Command-Line Format --slave-exec-mode=mode
    System Variable slave_exec_mode
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Enumeration
    Default Value

    IDEMPOTENT (NDB)

    STRICT (Other)

    Valid Values

    STRICT

    IDEMPOTENT

    From MySQL 8.0.26, slave_exec_mode is deprecated and the alias replica_exec_mode should be used instead. In releases before MySQL 8.0.26, use slave_exec_mode.

    slave_exec_mode controls how a replication thread resolves conflicts and errors during replication. IDEMPOTENT mode causes suppression of duplicate-key and no-key-found errors; STRICT means no such suppression takes place.

    IDEMPOTENT mode is intended for use in multi-source replication, circular replication, and some other special replication scenarios for NDB Cluster Replication. (See Section 23.7.10, 鈥淣DB Cluster Replication: Bidirectional and Circular Replication鈥?/a>, and Section 23.7.11, 鈥淣DB Cluster Replication Conflict Resolution鈥?/a>, for more information.) NDB Cluster ignores any value explicitly set for slave_exec_mode, and always treats it as IDEMPOTENT.

    In MySQL Server 8.0, STRICT mode is the default value.

    Setting this variable takes immediate effect for all replication channels, including running channels.

    For storage engines other than NDB, IDEMPOTENT mode should be used only when you are absolutely sure that duplicate-key errors and key-not-found errors can safely be ignored. It is meant to be used in fail-over scenarios for NDB Cluster where multi-source replication or circular replication is employed, and is not recommended for use in other cases.

  • slave_load_tmpdir

    Command-Line Format --slave-load-tmpdir=dir_name
    Deprecated 8.0.26
    System Variable slave_load_tmpdir
    Scope Global
    Dynamic No
    SET_VAR Hint Applies No
    Type Directory name
    Default Value Value of --tmpdir

    From MySQL 8.0.26, slave_load_tmpdir is deprecated and the alias replica_load_tmpdir should be used instead. In releases before MySQL 8.0.26, use slave_load_tmpdir.

    slave_load_tmpdir specifies the name of the directory where the replica creates temporary files. Setting this variable takes effect for all replication channels immediately, including running channels. The variable value is by default equal to the value of the tmpdir system variable, or the default that applies when that system variable is not specified.

    When the replication SQL thread replicates a LOAD DATA statement, it extracts the file to be loaded from the relay log into temporary files, and then loads these into the table. If the file loaded on the source is huge, the temporary files on the replica are huge, too. Therefore, it might be advisable to use this option to tell the replica to put temporary files in a directory located in some file system that has a lot of available space. In that case, the relay logs are huge as well, so you might also want to set the relay_log system variable to place the relay logs in that file system.

    The directory specified by this option should be located in a disk-based file system (not a memory-based file system) so that the temporary files used to replicate LOAD DATA statements can survive machine restarts. The directory also should not be one that is cleared by the operating system during the system startup process. However, replication can now continue after a restart if the temporary files have been removed.

  • slave_max_allowed_packet

    Command-Line Format --slave-max-allowed-packet=#
    Deprecated 8.0.26
    System Variable slave_max_allowed_packet
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Integer
    Default Value 1073741824
    Minimum Value 1024
    Maximum Value 1073741824
    Unit bytes
    Block Size 1024

    From MySQL 8.0.26, slave_max_allowed_packet is deprecated and the alias replica_max_allowed_packet should be used instead. In releases before MySQL 8.0.26, use slave_max_allowed_packet.

    slave_max_allowed_packet sets the maximum packet size in bytes that the replication SQL (applier) and I/O (receiver) threads can handle. Setting this variable takes effect for all replication channels immediately, including running channels. It is possible for a source to write binary log events longer than its max_allowed_packet setting once the event header is added. The setting for slave_max_allowed_packet must be larger than the max_allowed_packet setting on the source, so that large updates using row-based replication do not cause replication to fail.

    This global variable always has a value that is a positive integer multiple of 1024; if you set it to some value that is not, the value is rounded down to the next highest multiple of 1024 for it is stored or used; setting slave_max_allowed_packet to 0 causes 1024 to be used. (A truncation warning is issued in all such cases.) The default and maximum value is 1073741824 (1 GB); the minimum is 1024.

  • slave_net_timeout

    Command-Line Format --slave-net-timeout=#
    Deprecated 8.0.26
    System Variable slave_net_timeout
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Integer
    Default Value 60
    Minimum Value 1
    Maximum Value 31536000
    Unit seconds

    From MySQL 8.0.26, slave_net_timeout is deprecated and the alias replica_net_timeout should be used instead. In releases before MySQL 8.0.26, use slave_net_timeout.

    slave_net_timeout specifies the number of seconds to wait for more data or a heartbeat signal from the source before the replica considers the connection broken, aborts the read, and tries to reconnect. Setting this variable has no immediate effect. The state of the variable applies on all subsequent START REPLICA commands.

    The default value is 60 seconds (one minute). The first retry occurs immediately after the timeout. The interval between retries is controlled by the SOURCE_CONNECT_RETRY | MASTER_CONNECT_RETRY option for the CHANGE REPLICATION SOURCE TO | CHANGE MASTER TO statement, and the number of reconnection attempts is limited by the SOURCE_RETRY_COUNT | MASTER_RETRY_COUNT option.

    The heartbeat interval, which stops the connection timeout occurring in the absence of data if the connection is still good, is controlled by the SOURCE_HEARTBEAT_PERIOD | MASTER_HEARTBEAT_PERIOD option for the CHANGE REPLICATION SOURCE TO | CHANGE MASTER TO statement. The heartbeat interval defaults to half the value of slave_net_timeout, and it is recorded in the replica's connection metadata repository and shown in the replication_connection_configuration Performance Schema table. Note that a change to the value or default setting of slave_net_timeout does not automatically change the heartbeat interval, whether that has been set explicitly or is using a previously calculated default. If the connection timeout is changed, you must also issue CHANGE REPLICATION SOURCE TO | CHANGE MASTER TO to adjust the heartbeat interval to an appropriate value so that it occurs before the connection timeout.

  • slave_parallel_type

    Command-Line Format --slave-parallel-type=value
    Deprecated 8.0.26
    System Variable slave_parallel_type
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Enumeration
    Default Value (鈮?8.0.27) LOGICAL_CLOCK
    Default Value (鈮?8.0.26) DATABASE
    Valid Values

    DATABASE

    LOGICAL_CLOCK

    From MySQL 8.0.26, slave_parallel_type is deprecated and the alias replica_parallel_type should be used instead. In releases before MySQL 8.0.26, use slave_parallel_type.

    For multithreaded replicas (replicas on which replica_parallel_workers or slave_parallel_workers is set to a value greater than 0), slave_parallel_type specifies the policy used to decide which transactions are allowed to execute in parallel on the replica. The variable has no effect on replicas for which multithreading is not enabled. The possible values are:

    • LOGICAL_CLOCK: Transactions that are part of the same binary log group commit on a source are applied in parallel on a replica. The dependencies between transactions are tracked based on their timestamps to provide additional parallelization where possible. When this value is set, the binlog_transaction_dependency_tracking system variable can be used on the source to specify that write sets are used for parallelization in place of timestamps, if a write set is available for the transaction and gives improved results compared to timestamps.

    • DATABASE: Transactions that update different databases are applied in parallel. This value is only appropriate if data is partitioned into multiple databases which are being updated independently and concurrently on the source. There must be no cross-database constraints, as such constraints may be violated on the replica.

    When replica_preserve_commit_order=ON or slave_preserve_commit_order=ON is set, you can only use LOGICAL_CLOCK. Before MySQL 8.0.27, DATABASE is the default. From MySQL 8.0.27, multithreading is enabled by default for replica servers (replica_parallel_workers=4 by default), so LOGICAL_CLOCK is the default, and the setting replica_preserve_commit_order=ON is also the default.

    When your replication topology uses multiple levels of replicas, LOGICAL_CLOCK may achieve less parallelization for each level the replica is away from the source. You can reduce this effect by using binlog_transaction_dependency_tracking on the source to specify that write sets are used instead of timestamps for parallelization where possible.

    When binary log transaction compression is enabled using the binlog_transaction_compression system variable, if replica_parallel_type or slave_parallel_type is set to DATABASE, all the databases affected by the transaction are mapped before the transaction is scheduled. The use of binary log transaction compression with the DATABASE policy can reduce parallelism compared to uncompressed transactions, which are mapped and scheduled for each event.

  • slave_parallel_workers

    Command-Line Format --slave-parallel-workers=#
    Deprecated 8.0.26
    System Variable slave_parallel_workers
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Integer
    Default Value (鈮?8.0.27) 4
    Default Value (鈮?8.0.26) 0
    Minimum Value 0
    Maximum Value 1024

    From MySQL 8.0.26, slave_parallel_workers is deprecated and the alias replica_parallel_workers should be used instead. In releases before MySQL 8.0.26, use slave_parallel_workers.

    slave_parallel_workers enables multithreading on the replica and sets the number of applier threads for executing replication transactions in parallel. When the value is a number greater than 0, the replica is a multithreaded replica with the specified number of applier threads, plus a coordinator thread to manage them. If you are using multiple replication channels, each channel has this number of threads.

    Before MySQL 8.0.27, the default for this system variable is 0, so replicas are not multithreaded by default. From MySQL 8.0.27, the default is 4, so replicas are multithreaded by default.

    Retrying of transactions is supported when multithreading is enabled on a replica. When replica_preserve_commit_order=ON or slave_preserve_commit_order=ON is set, transactions on a replica are externalized on the replica in the same order as they appear in the replica's relay log. The way in which transactions are distributed among applier threads is configured by replica_parallel_type (from MySQL 8.0.26) or slave_parallel_type (before MySQL 8.0.26). From MySQL 8.0.27, these system variables also have appropriate defaults for multithreading.

    To disable parallel execution, set replica_parallel_workers to 0, which gives the replica a single applier thread and no coordinator thread. With this setting, the replica_parallel_type or slave_parallel_type and replica_preserve_commit_order or slave_preserve_commit_order system variables have no effect and are ignored. From MySQL 8.0.27, if parallel execution is disabled when the CHANGE REPLICATION SOURCE TO option GTID_ONLY is enabled on a replica, the replica actually uses one parallel worker to take advantage of the method for retrying transactions without accessing the file positions. With one parallel worker, the replica_preserve_commit_order (slave_preserve_commit_order) system variable also has no effect.

    Setting replica_parallel_workers has no immediate effect. The state of the variable applies on all subsequent START REPLICA statements.

    Multithreaded replicas are not currently supported by NDB Cluster. See Section 23.7.3, 鈥淜nown Issues in NDB Cluster Replication鈥?/a>, for more information about how NDB handles settings for this variable.

  • slave_pending_jobs_size_max

    Command-Line Format --slave-pending-jobs-size-max=#
    Deprecated 8.0.26
    System Variable slave_pending_jobs_size_max
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Integer
    Default Value (鈮?8.0.12) 128M
    Default Value (8.0.11) 16M
    Minimum Value 1024
    Maximum Value 16EiB
    Unit bytes
    Block Size 1024

    From MySQL 8.0.26, slave_pending_jobs_size_max is deprecated and the alias replica_pending_jobs_size_max should be used instead. In releases before MySQL 8.0.26, use slave_pending_jobs_size_max.

    For multithreaded replicas, this variable sets the maximum amount of memory (in bytes) available to applier queues holding events not yet applied. Setting this variable has no effect on replicas for which multithreading is not enabled. Setting this variable has no immediate effect. The state of the variable applies on all subsequent START REPLICA commands.

    The minimum possible value for this variable is 1024 bytes; the default is 128MB. The maximum possible value is 18446744073709551615 (16 exbibytes). Values that are not exact multiples of 1024 bytes are rounded down to the next lower multiple of 1024 bytes prior to being stored.

    The value of this variable is a soft limit and can be set to match the normal workload. If an unusually large event exceeds this size, the transaction is held until all the worker threads have empty queues, and then processed. All subsequent transactions are held until the large transaction has been completed.

  • slave_preserve_commit_order

    Command-Line Format --slave-preserve-commit-order[={OFF|ON}]
    Deprecated 8.0.26
    System Variable slave_preserve_commit_order
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Boolean
    Default Value (鈮?8.0.27) ON
    Default Value (鈮?8.0.26) OFF

    From MySQL 8.0.26, slave_preserve_commit_order is deprecated and the alias replica_preserve_commit_order should be used instead. In releases before MySQL 8.0.26, use slave_preserve_commit_order.

    For multithreaded replicas (replicas on which replica_parallel_workers or slave_parallel_workers is set to a value greater than 0), setting slave_preserve_commit_order=1 ensures that transactions are executed and committed on the replica in the same order as they appear in the replica's relay log. This prevents gaps in the sequence of transactions that have been executed from the replica's relay log, and preserves the same transaction history on the replica as on the source (with the limitations listed below). This variable has no effect on replicas for which multithreading is not enabled.

    Before MySQL 8.0.27, the default for this system variable is OFF, meaning that transactions may be committed out of order. From MySQL 8.0.27, multithreading is enabled by default for replica servers (replica_parallel_workers=4 by default), so slave_preserve_commit_order=ON is the default, and the setting slave_parallel_type=LOGICAL_CLOCK is also the default. Also from MySQL 8.0.27, the setting for slave_preserve_commit_order is ignored if slave_parallel_workers is set to 1, because in that situation the order of transactions is preserved anyway.

    Up to and including MySQL 8.0.18, setting slave_preserve_commit_order=ON requires that binary logging (log_bin) and replica update logging (log_slave_updates) are enabled on the replica, which are the default settings from MySQL 8.0. From MySQL 8.0.19, binary logging and replica update logging are not required on the replica to set slave_preserve_commit_order=ON, and can be disabled if wanted. In all releases, setting slave_preserve_commit_order=ON requires that slave_parallel_type is set to LOGICAL_CLOCK, which is not the default setting before MySQL 8.0.27. Before changing the value of slave_preserve_commit_order and slave_parallel_type, the replication SQL thread (for all replication channels if you are using multiple replication channels) must be stopped.

    When slave_preserve_commit_order=OFF is set, which is the default, the transactions that a multithreaded replica applies in parallel may commit out of order. Therefore, checking for the most recently executed transaction does not guarantee that all previous transactions from the source have been executed on the replica. There is a chance of gaps in the sequence of transactions that have been executed from the replica's relay log. This has implications for logging and recovery when using a multithreaded replica. See Section 17.5.1.34, 鈥淩eplication and Transaction Inconsistencies鈥?/a> for more information.

    When slave_preserve_commit_order=ON is set, the executing worker thread waits until all previous transactions are committed before committing. While a given thread is waiting for other worker threads to commit their transactions, it reports its status as Waiting for preceding transaction to commit. With this mode, a multithreaded replica never enters a state that the source was not in. This supports the use of replication for read scale-out. See Section 17.4.5, 鈥淯sing Replication for Scale-Out鈥?/a>.

    Note
    • slave_preserve_commit_order=ON does not prevent source binary log position lag, where Exec_master_log_pos is behind the position up to which transactions have been executed. See Section 17.5.1.34, 鈥淩eplication and Transaction Inconsistencies鈥?/a>.

    • slave_preserve_commit_order=ON does not preserve the commit order and transaction history if the replica uses filters on its binary log, such as --binlog-do-db.

    • slave_preserve_commit_order=ON does not preserve the order of non-transactional DML updates. These might commit before transactions that precede them in the relay log, which might result in gaps in the sequence of transactions that have been executed from the replica's relay log.

    • In releases before MySQL 8.0.19, slave_preserve_commit_order=ON does not preserve the order of statements with an IF EXISTS clause when the object concerned does not exist. These might commit before transactions that precede them in the relay log, which might result in gaps in the sequence of transactions that have been executed from the replica's relay log.

    • A limitation to preserving the commit order on the replica can occur if statement-based replication is in use, and both transactional and non-transactional storage engines participate in a non-XA transaction that is rolled back on the source. Normally, non-XA transactions that are rolled back on the source are not replicated to the replica, but in this particular situation, the transaction might be replicated to the replica. If this does happen, a multithreaded replica without binary logging does not handle the transaction rollback, so the commit order on the replica diverges from the relay log order of the transactions in that case.

  • slave_rows_search_algorithms

    Command-Line Format --slave-rows-search-algorithms=value
    Deprecated 8.0.18
    System Variable slave_rows_search_algorithms
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Set
    Default Value INDEX_SCAN,HASH_SCAN
    Valid Values

    TABLE_SCAN,INDEX_SCAN

    INDEX_SCAN,HASH_SCAN

    TABLE_SCAN,HASH_SCAN

    TABLE_SCAN,INDEX_SCAN,HASH_SCAN (equivalent to INDEX_SCAN,HASH_SCAN)

    When preparing batches of rows for row-based logging and replication, this system variable controls how the rows are searched for matches, in particular whether hash scans are used. The use of this system variable is now deprecated. The default setting INDEX_SCAN,HASH_SCAN is optimal for performance and works correctly in all scenarios. See Section 17.5.1.27, 鈥淩eplication and Row Searches鈥?/a>.

  • slave_skip_errors

    Command-Line Format --slave-skip-errors=name
    Deprecated 8.0.26
    System Variable slave_skip_errors
    Scope Global
    Dynamic No
    SET_VAR Hint Applies No
    Type String
    Default Value OFF
    Valid Values

    OFF

    [list of error codes]

    all

    ddl_exist_errors

    From MySQL 8.0.26, slave_skip_errors is deprecated and the alias replica_skip_errors should be used instead. In releases before MySQL 8.0.26, use slave_skip_errors.

    Normally, replication stops when an error occurs on the replica, which gives you the opportunity to resolve the inconsistency in the data manually. This variable causes the replication SQL thread to continue replication when a statement returns any of the errors listed in the variable value.

  • replica_skip_errors

    Command-Line Format --replica-skip-errors=name
    Introduced 8.0.26
    System Variable replica_skip_errors
    Scope Global
    Dynamic No
    SET_VAR Hint Applies No
    Type String
    Default Value OFF
    Valid Values

    OFF

    [list of error codes]

    all

    ddl_exist_errors

    From MySQL 8.0.26, use replica_skip_errors in place of slave_skip_errors, which is deprecated from that release. In releases before MySQL 8.0.26, use slave_skip_errors.

    Normally, replication stops when an error occurs on the replica, which gives you the opportunity to resolve the inconsistency in the data manually. This variable causes the replication SQL thread to continue replication when a statement returns any of the errors listed in the variable value.

  • slave_sql_verify_checksum

    Command-Line Format --slave-sql-verify-checksum[={OFF|ON}]
    Deprecated 8.0.26
    System Variable slave_sql_verify_checksum
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Boolean
    Default Value ON

    From MySQL 8.0.26, slave_sql_verify_checksum is deprecated and the alias replica_sql_verify_checksum should be used instead. In releases before MySQL 8.0.26, use slave_sql_verify_checksum.

    slave_sql_verify_checksum causes the replication SQL thread to verify data using the checksums read from the relay log. In the event of a mismatch, the replica stops with an error. Setting this variable takes effect for all replication channels immediately, including running channels.

    Note

    The replication I/O (receiver) thread always reads checksums if possible when accepting events from over the network.

  • slave_transaction_retries

    Command-Line Format --slave-transaction-retries=#
    Deprecated 8.0.26
    System Variable slave_transaction_retries
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Integer
    Default Value 10
    Minimum Value 0
    Maximum Value (64-bit platforms) 18446744073709551615
    Maximum Value (32-bit platforms) 4294967295

    From MySQL 8.0.26, slave_transaction_retries is deprecated and the alias replica_transaction_retries should be used instead. In releases before MySQL 8.0.26, use slave_transaction_retries.

    slave_transaction_retries sets the maximum number of times for replication SQL threads on a single-threaded or multithreaded replica to automatically retry failed transactions before stopping. Setting this variable takes effect for all replication channels immediately, including running channels. The default value is 10. Setting the variable to 0 disables automatic retrying of transactions.

    If a replication SQL thread fails to execute a transaction because of an InnoDB deadlock or because the transaction's execution time exceeded InnoDB's innodb_lock_wait_timeout or NDB's TransactionDeadlockDetectionTimeout or TransactionInactiveTimeout, it automatically retries slave_transaction_retries times before stopping with an error. Transactions with a non-temporary error are not retried.

    The Performance Schema table replication_applier_status shows the number of retries that took place on each replication channel, in the COUNT_TRANSACTIONS_RETRIES column. The Performance Schema table replication_applier_status_by_worker shows detailed information on transaction retries by individual applier threads on a single-threaded or multithreaded replica, and identifies the errors that caused the last transaction and the transaction currently in progress to be reattempted.

  • slave_type_conversions

    Command-Line Format --slave-type-conversions=set
    Deprecated 8.0.26
    System Variable slave_type_conversions
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Set
    Default Value
    Valid Values

    ALL_LOSSY

    ALL_NON_LOSSY

    ALL_SIGNED

    ALL_UNSIGNED

    From MySQL 8.0.26, slave_type_conversions is deprecated and the alias replica_type_conversions should be used instead. In releases before MySQL 8.0.26, use slave_type_conversions.

    slave_type_conversions controls the type conversion mode in effect on the replica when using row-based replication. Its value is a comma-delimited set of zero or more elements from the list: ALL_LOSSY, ALL_NON_LOSSY, ALL_SIGNED, ALL_UNSIGNED. Set this variable to an empty string to disallow type conversions between the source and the replica. Setting this variable takes effect for all replication channels immediately, including running channels.

    For additional information on type conversion modes applicable to attribute promotion and demotion in row-based replication, see Row-based replication: attribute promotion and demotion.

  • sql_replica_skip_counter

    Introduced 8.0.26
    System Variable sql_replica_skip_counter
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Integer
    Default Value 0
    Minimum Value 0
    Maximum Value 4294967295

    From MySQL 8.0.26, use sql_replica_skip_counter in place of sql_slave_skip_counter, which is deprecated from that release. In releases before MySQL 8.0.26, use sql_slave_skip_counter.

    sql_replica_skip_counter specifies the number of events from the source that a replica should skip. Setting the option has no immediate effect. The variable applies to the next START REPLICA statement; the next START REPLICA statement also changes the value back to 0. When this variable is set to a nonzero value and there are multiple replication channels configured, the START REPLICA statement can only be used with the FOR CHANNEL channel clause.

    This option is incompatible with GTID-based replication, and must not be set to a nonzero value when gtid_mode=ON is set. If you need to skip transactions when employing GTIDs, use gtid_executed from the source instead. If you have enabled GTID assignment on a replication channel using the ASSIGN_GTIDS_TO_ANONYMOUS_TRANSACTIONS option of the CHANGE REPLICATION SOURCE TO statement, sql_replica_skip_counter is available. See Section 17.1.7.3, 鈥淪kipping Transactions鈥?/a>.

  • sql_slave_skip_counter

    Deprecated 8.0.26
    System Variable sql_slave_skip_counter
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Integer
    Default Value 0
    Minimum Value 0
    Maximum Value 4294967295

    From MySQL 8.0.26, sql_slave_skip_counter is deprecated and the alias sql_replica_skip_counter should be used instead. In releases before MySQL 8.0.26, use sql_slave_skip_counter.

    sql_slave_skip_counter specifies the number of events from the source that a replica should skip. Setting the option has no immediate effect. The variable applies to the next START REPLICA statement; the next START REPLICA statement also changes the value back to 0. When this variable is set to a nonzero value and there are multiple replication channels configured, the START REPLICA statement can only be used with the FOR CHANNEL channel clause.

    This option is incompatible with GTID-based replication, and must not be set to a nonzero value when gtid_mode=ON is set. If you need to skip transactions when employing GTIDs, use gtid_executed from the source instead. If you have enabled GTID assignment on a replication channel using the ASSIGN_GTIDS_TO_ANONYMOUS_TRANSACTIONS option of the CHANGE REPLICATION SOURCE TO statement, sql_slave_skip_counter is available. See Section 17.1.7.3, 鈥淪kipping Transactions鈥?/a>.

  • sync_master_info

    Command-Line Format --sync-master-info=#
    Deprecated 8.0.26
    System Variable sync_master_info
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Integer
    Default Value 10000
    Minimum Value 0
    Maximum Value 4294967295

    From MySQL 8.0.26, sync_master_info is deprecated and the alias sync_source_info should be used instead. In releases before MySQL 8.0.26, use sync_master_info.

    sync_master_info specifies the number of events after which the replica updates the connection metadata repository. When the connection metadata repository is stored as an InnoDB table, which is the default from MySQL 8.0, it is updated after this number of events. If the connection metadata repository is stored as a file, which is deprecated from MySQL 8.0, the replica synchronizes its master.info file to disk (using fdatasync()) after this number of events. The default value is 10000, and a zero value means that the repository is never updated. Setting this variable takes effect for all replication channels immediately, including running channels.

  • sync_relay_log

    Command-Line Format --sync-relay-log=#
    System Variable sync_relay_log
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Integer
    Default Value 10000
    Minimum Value 0
    Maximum Value 4294967295

    If the value of this variable is greater than 0, the MySQL server synchronizes its relay log to disk (using fdatasync()) after every sync_relay_log events are written to the relay log. Setting this variable takes effect for all replication channels immediately, including running channels.

    Setting sync_relay_log to 0 causes no synchronization to be done to disk; in this case, the server relies on the operating system to flush the relay log's contents from time to time as for any other file.

    A value of 1 is the safest choice because in the event of an unexpected halt you lose at most one event from the relay log. However, it is also the slowest choice (unless the disk has a battery-backed cache, which makes synchronization very fast). For information on the combination of settings on a replica that is most resilient to unexpected halts, see Section 17.4.2, 鈥淗andling an Unexpected Halt of a Replica鈥?/a>.

  • sync_relay_log_info

    Command-Line Format --sync-relay-log-info=#
    System Variable sync_relay_log_info
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Integer
    Default Value 10000
    Minimum Value 0
    Maximum Value 4294967295

    The number of transactions after which the replica updates the applier metadata repository. When the applier metadata repository is stored as an InnoDB table, which is the default from MySQL 8.0, it is updated after every transaction and this system variable is ignored. If the applier metadata repository is stored as a file, which is deprecated from MySQL 8.0, the replica synchronizes its relay-log.info file to disk (using fdatasync()) after this number of transactions. The default value for sync_relay_log_info is 10000, and a zero value means that the file contents are only flushed by the operating system. Setting this variable takes effect for all replication channels immediately, including running channels.

  • sync_source_info

    Command-Line Format --sync-source-info=#
    Introduced 8.0.26
    System Variable sync_source_info
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Integer
    Default Value 10000
    Minimum Value 0
    Maximum Value 4294967295

    From MySQL 8.0.26, use sync_source_info in place of sync_master_info, which is deprecated from that release. In releases before MySQL 8.0.26, use sync_source_info.

    sync_source_info specifies the number of events after which the replica updates the connection metadata repository. When the connection metadata repository is stored as an InnoDB table, which is the default from MySQL 8.0, it is updated after this number of events. If the connection metadata repository is stored as a file, which is deprecated from MySQL 8.0, the replica synchronizes its master.info file to disk (using fdatasync()) after this number of events. The default value is 10000, and a zero value means that the repository is never updated. Setting this variable takes effect for all replication channels immediately, including running channels.

  • terminology_use_previous

    Command-Line Format --terminology-use-previous=#
    Introduced 8.0.26
    System Variable terminology_use_previous
    Scope Global, Session
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Enumeration
    Default Value NONE
    Valid Values

    NONE

    BEFORE_8_0_26

    In MySQL 8.0.26, incompatible changes were made to instrumentation names containing the terms 鈥?span class="quote">master鈥?/span>, which is changed to 鈥?span class="quote">source鈥?/span>, 鈥?span class="quote">slave鈥?/span>, which is changed to 鈥?span class="quote">replica鈥?/span>, and 鈥?span class="quote">mts鈥?/span> (for 鈥?span class="quote">multithreaded slave鈥?/span>), which is changed to 鈥?span class="quote">mta鈥?/span> (for 鈥?span class="quote">multithreaded applier鈥?/span>). Monitoring tools that work with these instrumentation names might be impacted. If the incompatible changes have an impact for you, set the terminology_use_previous system variable to BEFORE_8_0_26 to make MySQL Server use the old versions of the names for the objects specified in the previous list. This enables monitoring tools that rely on the old names to continue working until they can be updated to use the new names.

    Set the terminology_use_previous system variable with session scope to support individual functions, or global scope to be a default for all new sessions. When global scope is used, the slow query log contains the old versions of the names.

    The affected instrumentation names are given in the following list. The terminology_use_previous system variable only affects these items. It does not affect the new aliases for system variables, status variables, and command-line options that were also introduced in MySQL 8.0.26, and these can still be used when it is set.

    • Instrumented locks (mutexes), visible in the mutex_instances and events_waits_* Performance Schema tables with the prefix wait/synch/mutex/

    • Read/write locks, visible in the rwlock_instances and events_waits_* Performance Schema tables with the prefix wait/synch/rwlock/

    • Instrumented condition variables, visible in the cond_instances and events_waits_* Performance Schema tables with the prefix wait/synch/cond/

    • Instrumented memory allocations, visible in the memory_summary_* Performance Schema tables with the prefix memory/sql/

    • Thread names, visible in the threads Performance Schema table with the prefix thread/sql/

    • Thread stages, visible in the events_stages_* Performance Schema tables with the prefix stage/sql/, and without the prefix in the threads and processlist Performance Schema tables, the output from the SHOW PROCESSLIST statement, the Information Schema processlist table, and the slow query log

    • Thread commands, visible in the events_statements_history* and events_statements_summary_*_by_event_name Performance Schema tables with the prefix statement/com/, and without the prefix in the threads and processlist Performance Schema tables, the output from the SHOW PROCESSLIST statement, the Information Schema processlist table, and the output from the SHOW REPLICA STATUS statement


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MySQL 8.0 Reference Manual  /  ...  /  Replication and Binary Logging Options and Variables

17.1.6 Replication and Binary Logging Options and Variables

The following sections contain information about mysqld options and server variables that are used in replication and for controlling the binary log. Options and variables for use on sources and replicas are covered separately, as are options and variables relating to binary logging and global transaction identifiers (GTIDs). A set of quick-reference tables providing basic information about these options and variables is also included.

Of particular importance is the server_id system variable.

Command-Line Format --server-id=#
System Variable server_id
Scope Global
Dynamic Yes
SET_VAR Hint Applies No
Type Integer
Default Value 1
Minimum Value 0
Maximum Value 4294967295

This variable specifies the server ID. server_id is set to 1 by default. The server can be started with this default ID, but when binary logging is enabled, an informational message is issued if you did not set server_id explicitly to specify a server ID.

For servers that are used in a replication topology, you must specify a unique server ID for each replication server, in the range from 1 to 232 鈭?1. 鈥?span class="quote">Unique鈥?/span> means that each ID must be different from every other ID in use by any other source or replica in the replication topology. For additional information, see Section 17.1.6.2, 鈥淩eplication Source Options and Variables鈥?/a>, and Section 17.1.6.3, 鈥淩eplica Server Options and Variables鈥?/a>.

If the server ID is set to 0, binary logging takes place, but a source with a server ID of 0 refuses any connections from replicas, and a replica with a server ID of 0 refuses to connect to a source. Note that although you can change the server ID dynamically to a nonzero value, doing so does not enable replication to start immediately. You must change the server ID and then restart the server to initialize the replica.

For more information, see Section 17.1.2.2, 鈥淪etting the Replica Configuration鈥?/a>.

server_uuid

The MySQL server generates a true UUID in addition to the default or user-supplied server ID set in the server_id system variable. This is available as the global, read-only variable server_uuid.

Note

The presence of the server_uuid system variable does not change the requirement for setting a unique server_id value for each MySQL server as part of preparing and running MySQL replication, as described earlier in this section.

System Variable server_uuid
Scope Global
Dynamic No
SET_VAR Hint Applies No
Type String

When starting, the MySQL server automatically obtains a UUID as follows:

  1. Attempt to read and use the UUID written in the file data_dir/auto.cnf (where data_dir is the server's data directory).

  2. If data_dir/auto.cnf is not found, generate a new UUID and save it to this file, creating the file if necessary.

The auto.cnf file has a format similar to that used for my.cnf or my.ini files. auto.cnf has only a single [auto] section containing a single server_uuid setting and value; the file's contents appear similar to what is shown here:

[auto]
server_uuid=8a94f357-aab4-11df-86ab-c80aa9429562
Important

The auto.cnf file is automatically generated; do not attempt to write or modify this file.

When using MySQL replication, sources and replicas know each other's UUIDs. The value of a replica's UUID can be seen in the output of SHOW REPLICAS (or before MySQL 8.0.22, SHOW SLAVE HOSTS). Once START REPLICA has been executed, the value of the source's UUID is available on the replica in the output of SHOW REPLICA STATUS. As of 8.0.22, the keyword SLAVE was replaced by REPLICA.

Note

Issuing a STOP REPLICA or RESET REPLICA statement does not reset the source's UUID as used on the replica.

A server's server_uuid is also used in GTIDs for transactions originating on that server. For more information, see Section 17.1.3, 鈥淩eplication with Global Transaction Identifiers鈥?/a>.

When starting, the replication I/O (receiver) thread generates an error and aborts if its source's UUID is equal to its own unless the --replicate-same-server-id option has been set. In addition, the replication receiver thread generates a warning if either of the following is true:


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MySQL 8.0 Reference Manual  /  ...  /  Replication Source Options and Variables

17.1.6.2 Replication Source Options and Variables

This section describes the server options and system variables that you can use on replication source servers. You can specify the options either on the command line or in an option file. You can specify system variable values using SET.

On the source and each replica, you must set the server_id system variable to establish a unique replication ID. For each server, you should pick a unique positive integer in the range from 1 to 232 鈭?1, and each ID must be different from every other ID in use by any other source or replica in the replication topology. Example: server-id=3.

For options used on the source for controlling binary logging, see Section 17.1.6.4, 鈥淏inary Logging Options and Variables鈥?/a>.

Startup Options for Replication Source Servers

The following list describes startup options for controlling replication source servers. Replication-related system variables are discussed later in this section.

System Variables Used on Replication Source Servers

The following system variables are used for or by replication source servers:

  • auto_increment_increment

    Command-Line Format --auto-increment-increment=#
    System Variable auto_increment_increment
    Scope Global, Session
    Dynamic Yes
    SET_VAR Hint Applies Yes
    Type Integer
    Default Value 1
    Minimum Value 1
    Maximum Value 65535

    auto_increment_increment and auto_increment_offset are intended for use with circular (source-to-source) replication, and can be used to control the operation of AUTO_INCREMENT columns. Both variables have global and session values, and each can assume an integer value between 1 and 65,535 inclusive. Setting the value of either of these two variables to 0 causes its value to be set to 1 instead. Attempting to set the value of either of these two variables to an integer greater than 65,535 or less than 0 causes its value to be set to 65,535 instead. Attempting to set the value of auto_increment_increment or auto_increment_offset to a noninteger value produces an error, and the actual value of the variable remains unchanged.

    Note

    auto_increment_increment is also supported for use with NDB tables.

    As of MySQL 8.0.18, setting the session value of this system variable is no longer a restricted operation.

    When Group Replication is started on a server, the value of auto_increment_increment is changed to the value of group_replication_auto_increment_increment, which defaults to 7, and the value of auto_increment_offset is changed to the server ID. The changes are reverted when Group Replication is stopped. These changes are only made and reverted if auto_increment_increment and auto_increment_offset each have their default value of 1. If their values have already been modified from the default, Group Replication does not alter them. From MySQL 8.0, the system variables are also not modified when Group Replication is in single-primary mode, where only one server writes.

    auto_increment_increment and auto_increment_offset affect AUTO_INCREMENT column behavior as follows:

    • auto_increment_increment controls the interval between successive column values. For example:

      mysql> SHOW VARIABLES LIKE 'auto_inc%';
      +--------------------------+-------+
      | Variable_name            | Value |
      +--------------------------+-------+
      | auto_increment_increment | 1     |
      | auto_increment_offset    | 1     |
      +--------------------------+-------+
      2 rows in set (0.00 sec)
      
      mysql> CREATE TABLE autoinc1
          -> (col INT NOT NULL AUTO_INCREMENT PRIMARY KEY);
        Query OK, 0 rows affected (0.04 sec)
      
      mysql> SET @@auto_increment_increment=10;
      Query OK, 0 rows affected (0.00 sec)
      
      mysql> SHOW VARIABLES LIKE 'auto_inc%';
      +--------------------------+-------+
      | Variable_name            | Value |
      +--------------------------+-------+
      | auto_increment_increment | 10    |
      | auto_increment_offset    | 1     |
      +--------------------------+-------+
      2 rows in set (0.01 sec)
      
      mysql> INSERT INTO autoinc1 VALUES (NULL), (NULL), (NULL), (NULL);
      Query OK, 4 rows affected (0.00 sec)
      Records: 4  Duplicates: 0  Warnings: 0
      
      mysql> SELECT col FROM autoinc1;
      +-----+
      | col |
      +-----+
      |   1 |
      |  11 |
      |  21 |
      |  31 |
      +-----+
      4 rows in set (0.00 sec)
    • auto_increment_offset determines the starting point for the AUTO_INCREMENT column value. Consider the following, assuming that these statements are executed during the same session as the example given in the description for auto_increment_increment:

      mysql> SET @@auto_increment_offset=5;
      Query OK, 0 rows affected (0.00 sec)
      
      mysql> SHOW VARIABLES LIKE 'auto_inc%';
      +--------------------------+-------+
      | Variable_name            | Value |
      +--------------------------+-------+
      | auto_increment_increment | 10    |
      | auto_increment_offset    | 5     |
      +--------------------------+-------+
      2 rows in set (0.00 sec)
      
      mysql> CREATE TABLE autoinc2
          -> (col INT NOT NULL AUTO_INCREMENT PRIMARY KEY);
      Query OK, 0 rows affected (0.06 sec)
      
      mysql> INSERT INTO autoinc2 VALUES (NULL), (NULL), (NULL), (NULL);
      Query OK, 4 rows affected (0.00 sec)
      Records: 4  Duplicates: 0  Warnings: 0
      
      mysql> SELECT col FROM autoinc2;
      +-----+
      | col |
      +-----+
      |   5 |
      |  15 |
      |  25 |
      |  35 |
      +-----+
      4 rows in set (0.02 sec)

      When the value of auto_increment_offset is greater than that of auto_increment_increment, the value of auto_increment_offset is ignored.

    If either of these variables is changed, and then new rows inserted into a table containing an AUTO_INCREMENT column, the results may seem counterintuitive because the series of AUTO_INCREMENT values is calculated without regard to any values already present in the column, and the next value inserted is the least value in the series that is greater than the maximum existing value in the AUTO_INCREMENT column. The series is calculated like this:

    auto_increment_offset + Nauto_increment_increment

    where N is a positive integer value in the series [1, 2, 3, ...]. For example:

    Press CTRL+C to copy
    mysql> SHOW VARIABLES LIKE 'auto_inc%'; +--------------------------+-------+ | Variable_name | Value | +--------------------------+-------+ | auto_increment_increment | 10 | | auto_increment_offset | 5 | +--------------------------+-------+ 2 rows in set (0.00 sec) mysql> SELECT col FROM autoinc1; +-----+ | col | +-----+ | 1 | | 11 | | 21 | | 31 | +-----+ 4 rows in set (0.00 sec) mysql> INSERT INTO autoinc1 VALUES (NULL), (NULL), (NULL), (NULL); Query OK, 4 rows affected (0.00 sec) Records: 4 Duplicates: 0 Warnings: 0 mysql> SELECT col FROM autoinc1; +-----+ | col | +-----+ | 1 | | 11 | | 21 | | 31 | | 35 | | 45 | | 55 | | 65 | +-----+ 8 rows in set (0.00 sec)

    The values shown for auto_increment_increment and auto_increment_offset generate the series 5 + N 脳 10, that is, [5, 15, 25, 35, 45, ...]. The highest value present in the col column prior to the INSERT is 31, and the next available value in the AUTO_INCREMENT series is 35, so the inserted values for col begin at that point and the results are as shown for the SELECT query.

    It is not possible to restrict the effects of these two variables to a single table; these variables control the behavior of all AUTO_INCREMENT columns in all tables on the MySQL server. If the global value of either variable is set, its effects persist until the global value is changed or overridden by setting the session value, or until mysqld is restarted. If the local value is set, the new value affects AUTO_INCREMENT columns for all tables into which new rows are inserted by the current user for the duration of the session, unless the values are changed during that session.

    The default value of auto_increment_increment is 1. See Section 17.5.1.1, 鈥淩eplication and AUTO_INCREMENT鈥?/a>.

  • auto_increment_offset

    Command-Line Format --auto-increment-offset=#
    System Variable auto_increment_offset
    Scope Global, Session
    Dynamic Yes
    SET_VAR Hint Applies Yes
    Type Integer
    Default Value 1
    Minimum Value 1
    Maximum Value 65535

    This variable has a default value of 1. If it is left with its default value, and Group Replication is started on the server in multi-primary mode, it is changed to the server ID. For more information, see the description for auto_increment_increment.

    Note

    auto_increment_offset is also supported for use with NDB tables.

    As of MySQL 8.0.18, setting the session value of this system variable is no longer a restricted operation.

  • immediate_server_version

    Introduced 8.0.14
    System Variable immediate_server_version
    Scope Session
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Integer
    Default Value 999999
    Minimum Value 0
    Maximum Value 999999

    For internal use by replication. This session system variable holds the MySQL Server release number of the server that is the immediate source in a replication topology (for example, 80014 for a MySQL 8.0.14 server instance). If this immediate server is at a release that does not support the session system variable, the value of the variable is set to 0 (UNKNOWN_SERVER_VERSION).

    The value of the variable is replicated from a source to a replica. With this information the replica can correctly process data originating from a source at an older release, by recognizing where syntax changes or semantic changes have occurred between the releases involved and handling these appropriately. The information can also be used in a Group Replication environment where one or more members of the replication group is at a newer release than the others. The value of the variable can be viewed in the binary log for each transaction (as part of the Gtid_log_event, or Anonymous_gtid_log_event if GTIDs are not in use on the server), and could be helpful in debugging cross-version replication issues.

    Setting the session value of this system variable is a restricted operation. The session user must have either the REPLICATION_APPLIER privilege (see Section 17.3.3, 鈥淩eplication Privilege Checks鈥?/a>), or privileges sufficient to set restricted session variables (see Section 5.1.9.1, 鈥淪ystem Variable Privileges鈥?/a>). However, note that the variable is not intended for users to set; it is set automatically by the replication infrastructure.

  • original_server_version

    Introduced 8.0.14
    System Variable original_server_version
    Scope Session
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Integer
    Default Value 999999
    Minimum Value 0
    Maximum Value 999999

    For internal use by replication. This session system variable holds the MySQL Server release number of the server where a transaction was originally committed (for example, 80014 for a MySQL 8.0.14 server instance). If this original server is at a release that does not support the session system variable, the value of the variable is set to 0 (UNKNOWN_SERVER_VERSION). Note that when a release number is set by the original server, the value of the variable is reset to 0 if the immediate server or any other intervening server in the replication topology does not support the session system variable, and so does not replicate its value.

    The value of the variable is set and used in the same ways as for the immediate_server_version system variable. If the value of the variable is the same as that for the immediate_server_version system variable, only the latter is recorded in the binary log, with an indicator that the original server version is the same.

    In a Group Replication environment, view change log events, which are special transactions queued by each group member when a new member joins the group, are tagged with the server version of the group member queuing the transaction. This ensures that the server version of the original donor is known to the joining member. Because the view change log events queued for a particular view change have the same GTID on all members, for this case only, instances of the same GTID might have a different original server version.

    Setting the session value of this system variable is a restricted operation. The session user must have either the REPLICATION_APPLIER privilege (see Section 17.3.3, 鈥淩eplication Privilege Checks鈥?/a>), or privileges sufficient to set restricted session variables (see Section 5.1.9.1, 鈥淪ystem Variable Privileges鈥?/a>). However, note that the variable is not intended for users to set; it is set automatically by the replication infrastructure.

  • rpl_semi_sync_master_enabled

    Command-Line Format --rpl-semi-sync-master-enabled[={OFF|ON}]
    System Variable rpl_semi_sync_master_enabled
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Boolean
    Default Value OFF

    Controls whether semisynchronous replication is enabled on the source server. To enable or disable the plugin, set this variable to ON or OFF (or 1 or 0), respectively. The default is OFF.

    This variable is available only if the source-side semisynchronous replication plugin is installed.

  • rpl_semi_sync_master_timeout

    Command-Line Format --rpl-semi-sync-master-timeout=#
    System Variable rpl_semi_sync_master_timeout
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Integer
    Default Value 10000
    Minimum Value 0
    Maximum Value 4294967295
    Unit milliseconds

    A value in milliseconds that controls how long the source waits on a commit for acknowledgment from a replica before timing out and reverting to asynchronous replication. The default value is 10000 (10 seconds).

    This variable is available only if the source-side semisynchronous replication plugin is installed.

  • rpl_semi_sync_master_trace_level

    Command-Line Format --rpl-semi-sync-master-trace-level=#
    System Variable rpl_semi_sync_master_trace_level
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Integer
    Default Value 32
    Minimum Value 0
    Maximum Value 4294967295

    The semisynchronous replication debug trace level on the source server. Four levels are defined:

    • 1 = general level (for example, time function failures)

    • 16 = detail level (more verbose information)

    • 32 = net wait level (more information about network waits)

    • 64 = function level (information about function entry and exit)

    This variable is available only if the source-side semisynchronous replication plugin is installed.

  • rpl_semi_sync_master_wait_for_slave_count

    Command-Line Format --rpl-semi-sync-master-wait-for-slave-count=#
    System Variable rpl_semi_sync_master_wait_for_slave_count
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Integer
    Default Value 1
    Minimum Value 1
    Maximum Value 65535

    The number of replica acknowledgments the source must receive per transaction before proceeding. By default rpl_semi_sync_master_wait_for_slave_count is 1, meaning that semisynchronous replication proceeds after receiving a single replica acknowledgment. Performance is best for small values of this variable.

    For example, if rpl_semi_sync_master_wait_for_slave_count is 2, then 2 replicas must acknowledge receipt of the transaction before the timeout period configured by rpl_semi_sync_master_timeout for semisynchronous replication to proceed. If fewer replicas acknowledge receipt of the transaction during the timeout period, the source reverts to normal replication.

    Note

    This behavior also depends on rpl_semi_sync_master_wait_no_slave

    This variable is available only if the source-side semisynchronous replication plugin is installed.

  • rpl_semi_sync_master_wait_no_slave

    Command-Line Format --rpl-semi-sync-master-wait-no-slave[={OFF|ON}]
    System Variable rpl_semi_sync_master_wait_no_slave
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Boolean
    Default Value ON

    Controls whether the source waits for the timeout period configured by rpl_semi_sync_master_timeout to expire, even if the replica count drops to less than the number of replicas configured by rpl_semi_sync_master_wait_for_slave_count during the timeout period.

    When the value of rpl_semi_sync_master_wait_no_slave is ON (the default), it is permissible for the replica count to drop to less than rpl_semi_sync_master_wait_for_slave_count during the timeout period. As long as enough replicas acknowledge the transaction before the timeout period expires, semisynchronous replication continues.

    When the value of rpl_semi_sync_master_wait_no_slave is OFF, if the replica count drops to less than the number configured in rpl_semi_sync_master_wait_for_slave_count at any time during the timeout period configured by rpl_semi_sync_master_timeout, the source reverts to normal replication.

    This variable is available only if the source-side semisynchronous replication plugin is installed.

  • rpl_semi_sync_master_wait_point

    Command-Line Format --rpl-semi-sync-master-wait-point=value
    System Variable rpl_semi_sync_master_wait_point
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Enumeration
    Default Value AFTER_SYNC
    Valid Values

    AFTER_SYNC

    AFTER_COMMIT

    This variable controls the point at which a semisynchronous replication source server waits for replica acknowledgment of transaction receipt before returning a status to the client that committed the transaction. These values are permitted:

    • AFTER_SYNC (the default): The source writes each transaction to its binary log and the replica, and syncs the binary log to disk. The source waits for replica acknowledgment of transaction receipt after the sync. Upon receiving acknowledgment, the source commits the transaction to the storage engine and returns a result to the client, which then can proceed.

    • AFTER_COMMIT: The source writes each transaction to its binary log and the replica, syncs the binary log, and commits the transaction to the storage engine. The source waits for replica acknowledgment of transaction receipt after the commit. Upon receiving acknowledgment, the source returns a result to the client, which then can proceed.

    The replication characteristics of these settings differ as follows:

    • With AFTER_SYNC, all clients see the committed transaction at the same time: After it has been acknowledged by the replica and committed to the storage engine on the source. Thus, all clients see the same data on the source.

      In the event of source failure, all transactions committed on the source have been replicated to the replica (saved to its relay log). An unexpected exit of the source server and failover to the replica is lossless because the replica is up to date. Note, however, that the source cannot be restarted in this scenario and must be discarded, because its binary log might contain uncommitted transactions that would cause a conflict with the replica when externalized after binary log recovery.

    • With AFTER_COMMIT, the client issuing the transaction gets a return status only after the server commits to the storage engine and receives replica acknowledgment. After the commit and before replica acknowledgment, other clients can see the committed transaction before the committing client.

      If something goes wrong such that the replica does not process the transaction, then in the event of an unexpected source server exit and failover to the replica, it is possible for such clients to see a loss of data relative to what they saw on the source.

    This variable is available only if the source-side semisynchronous replication plugin is installed.

    With the addition of rpl_semi_sync_master_wait_point in MySQL 5.7, a version compatibility constraint was created because it increments the semisynchronous interface version: Servers for MySQL 5.7 and higher do not work with semisynchronous replication plugins from older versions, nor do servers from older versions work with semisynchronous replication plugins for MySQL 5.7 and higher.

  • rpl_semi_sync_source_enabled

    Command-Line Format --rpl-semi-sync-source-enabled[={OFF|ON}]
    Introduced 8.0.26
    System Variable rpl_semi_sync_source_enabled
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Boolean
    Default Value OFF

    rpl_semi_sync_source_enabled is available when the rpl_semi_sync_source (semisync_source.so library) plugin was installed on the replica to set up semisynchronous replication. If the rpl_semi_sync_master plugin (semisync_master.so library) was installed, rpl_semi_sync_master_enabled is available instead.

    rpl_semi_sync_source_enabled controls whether semisynchronous replication is enabled on the source server. To enable or disable the plugin, set this variable to ON or OFF (or 1 or 0), respectively. The default is OFF.

  • rpl_semi_sync_source_timeout

    Command-Line Format --rpl-semi-sync-source-timeout=#
    Introduced 8.0.26
    System Variable rpl_semi_sync_source_timeout
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Integer
    Default Value 10000
    Minimum Value 0
    Maximum Value 4294967295
    Unit milliseconds

    rpl_semi_sync_source_timeout is available when the rpl_semi_sync_source (semisync_source.so library) plugin was installed on the replica to set up semisynchronous replication. If the rpl_semi_sync_master plugin (semisync_master.so library) was installed, rpl_semi_sync_master_timeout is available instead.

    rpl_semi_sync_source_timeout controls how long the source waits on a commit for acknowledgment from a replica before timing out and reverting to asynchronous replication. The value is specified in milliseconds, and the default value is 10000 (10 seconds).

  • rpl_semi_sync_source_trace_level

    Command-Line Format --rpl-semi-sync-source-trace-level=#
    Introduced 8.0.26
    System Variable rpl_semi_sync_source_trace_level
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Integer
    Default Value 32
    Minimum Value 0
    Maximum Value 4294967295

    rpl_semi_sync_source_trace_level is available when the rpl_semi_sync_source (semisync_source.so library) plugin was installed on the replica to set up semisynchronous replication. If the rpl_semi_sync_master plugin (semisync_master.so library) was installed, rpl_semi_sync_master_trace_level is available instead.

    rpl_semi_sync_source_trace_level specifies the semisynchronous replication debug trace level on the source server. Four levels are defined:

    • 1 = general level (for example, time function failures)

    • 16 = detail level (more verbose information)

    • 32 = net wait level (more information about network waits)

    • 64 = function level (information about function entry and exit)

  • rpl_semi_sync_source_wait_for_replica_count

    Command-Line Format --rpl-semi-sync-source-wait-for-replica-count=#
    Introduced 8.0.26
    System Variable rpl_semi_sync_source_wait_for_replica_count
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Integer
    Default Value 1
    Minimum Value 1
    Maximum Value 65535

    rpl_semi_sync_source_wait_for_replica_count is available when the rpl_semi_sync_source (semisync_source.so library) plugin was installed on the replica to set up semisynchronous replication. If the rpl_semi_sync_master plugin (semisync_master.so library) was installed, rpl_semi_sync_master_wait_for_slave_count is available instead.

    rpl_semi_sync_source_wait_for_replica_count specifies the number of replica acknowledgments the source must receive per transaction before proceeding. By default rpl_semi_sync_source_wait_for_replica_count is 1, meaning that semisynchronous replication proceeds after receiving a single replica acknowledgment. Performance is best for small values of this variable.

    For example, if rpl_semi_sync_source_wait_for_replica_count is 2, then 2 replicas must acknowledge receipt of the transaction before the timeout period configured by rpl_semi_sync_source_timeout for semisynchronous replication to proceed. If fewer replicas acknowledge receipt of the transaction during the timeout period, the source reverts to normal replication.

    Note

    This behavior also depends on rpl_semi_sync_source_wait_no_replica.

  • rpl_semi_sync_source_wait_no_replica

    Command-Line Format --rpl-semi-sync-source-wait-no-replica[={OFF|ON}]
    Introduced 8.0.26
    System Variable rpl_semi_sync_source_wait_no_replica
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Boolean
    Default Value ON

    rpl_semi_sync_source_wait_no_replica is available when the rpl_semi_sync_source (semisync_source.so library) plugin was installed on the replica to set up semisynchronous replication. If the rpl_semi_sync_master plugin (semisync_master.so library) was installed, rpl_semi_sync_source_wait_no_replica is available instead.

    rpl_semi_sync_source_wait_no_replica controls whether the source waits for the timeout period configured by rpl_semi_sync_source_timeout to expire, even if the replica count drops to less than the number of replicas configured by rpl_semi_sync_source_wait_for_replica_count during the timeout period.

    When the value of rpl_semi_sync_source_wait_no_replica is ON (the default), it is permissible for the replica count to drop to less than rpl_semi_sync_source_wait_for_replica_count during the timeout period. As long as enough replicas acknowledge the transaction before the timeout period expires, semisynchronous replication continues.

    When the value of rpl_semi_sync_source_wait_no_replica is OFF, if the replica count drops to less than the number configured in rpl_semi_sync_source_wait_for_replica_count at any time during the timeout period configured by rpl_semi_sync_source_timeout, the source reverts to normal replication.

  • rpl_semi_sync_source_wait_point

    Command-Line Format --rpl-semi-sync-source-wait-point=value
    Introduced 8.0.26
    System Variable rpl_semi_sync_source_wait_point
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Enumeration
    Default Value AFTER_SYNC
    Valid Values

    AFTER_SYNC

    AFTER_COMMIT

    rpl_semi_sync_source_wait_point is available when the rpl_semi_sync_source (semisync_source.so library) plugin was installed on the replica to set up semisynchronous replication. If the rpl_semi_sync_master plugin (semisync_master.so library) was installed, rpl_semi_sync_master_wait_point is available instead.

    rpl_semi_sync_source_wait_point controls the point at which a semisynchronous replication source server waits for replica acknowledgment of transaction receipt before returning a status to the client that committed the transaction. These values are permitted:

    • AFTER_SYNC (the default): The source writes each transaction to its binary log and the replica, and syncs the binary log to disk. The source waits for replica acknowledgment of transaction receipt after the sync. Upon receiving acknowledgment, the source commits the transaction to the storage engine and returns a result to the client, which then can proceed.

    • AFTER_COMMIT: The source writes each transaction to its binary log and the replica, syncs the binary log, and commits the transaction to the storage engine. The source waits for replica acknowledgment of transaction receipt after the commit. Upon receiving acknowledgment, the source returns a result to the client, which then can proceed.

    The replication characteristics of these settings differ as follows:

    • With AFTER_SYNC, all clients see the committed transaction at the same time: After it has been acknowledged by the replica and committed to the storage engine on the source. Thus, all clients see the same data on the source.

      In the event of source failure, all transactions committed on the source have been replicated to the replica (saved to its relay log). An unexpected exit of the source server and failover to the replica is lossless because the replica is up to date. Note, however, that the source cannot be restarted in this scenario and must be discarded, because its binary log might contain uncommitted transactions that would cause a conflict with the replica when externalized after binary log recovery.

    • With AFTER_COMMIT, the client issuing the transaction gets a return status only after the server commits to the storage engine and receives replica acknowledgment. After the commit and before replica acknowledgment, other clients can see the committed transaction before the committing client.

      If something goes wrong such that the replica does not process the transaction, then in the event of an unexpected source server exit and failover to the replica, it is possible for such clients to see a loss of data relative to what they saw on the source.


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MySQL 8.0 Reference Manual  /  ...  /  Server Command Options

5.1.7 Server Command Options

When you start the mysqld server, you can specify program options using any of the methods described in Section 4.2.2, 鈥淪pecifying Program Options鈥?/a>. The most common methods are to provide options in an option file or on the command line. However, in most cases it is desirable to make sure that the server uses the same options each time it runs. The best way to ensure this is to list them in an option file. See Section 4.2.2.2, 鈥淯sing Option Files鈥?/a>. That section also describes option file format and syntax.

mysqld reads options from the [mysqld] and [server] groups. mysqld_safe reads options from the [mysqld], [server], [mysqld_safe], and [safe_mysqld] groups. mysql.server reads options from the [mysqld] and [mysql.server] groups.

mysqld accepts many command options. For a brief summary, execute this command:

Press CTRL+C to copy
mysqld --help

To see the full list, use this command:

Press CTRL+C to copy
mysqld --verbose --help

Some of the items in the list are actually system variables that can be set at server startup. These can be displayed at runtime using the SHOW VARIABLES statement. Some items displayed by the preceding mysqld command do not appear in SHOW VARIABLES output; this is because they are options only and not system variables.

The following list shows some of the most common server options. Additional options are described in other sections:

Some options control the size of buffers or caches. For a given buffer, the server might need to allocate internal data structures. These structures typically are allocated from the total memory allocated to the buffer, and the amount of space required might be platform dependent. This means that when you assign a value to an option that controls a buffer size, the amount of space actually available might differ from the value assigned. In some cases, the amount might be less than the value assigned. It is also possible that the server adjusts a value upward. For example, if you assign a value of 0 to an option for which the minimal value is 1024, the server sets the value to 1024.

Values for buffer sizes, lengths, and stack sizes are given in bytes unless otherwise specified.

Some options take file name values. Unless otherwise specified, the default file location is the data directory if the value is a relative path name. To specify the location explicitly, use an absolute path name. Suppose that the data directory is /var/mysql/data. If a file-valued option is given as a relative path name, it is located under /var/mysql/data. If the value is an absolute path name, its location is as given by the path name.

You can also set the values of server system variables at server startup by using variable names as options. To assign a value to a server system variable, use an option of the form --var_name=value. For example, --sort_buffer_size=384M sets the sort_buffer_size variable to a value of 384MB.

When you assign a value to a variable, MySQL might automatically correct the value to stay within a given range, or adjust the value to the closest permissible value if only certain values are permitted.

To restrict the maximum value to which a system variable can be set at runtime with the SET statement, specify this maximum by using an option of the form --maximum-var_name=value at server startup.

You can change the values of most system variables at runtime with the SET statement. See Section 13.7.6.1, 鈥淪ET Syntax for Variable Assignment鈥?/a>.

Section 5.1.8, 鈥淪erver System Variables鈥?/a>, provides a full description for all variables, and additional information for setting them at server startup and runtime. For information on changing system variables, see Section 5.1.1, 鈥淐onfiguring the Server鈥?/a>.


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MySQL 8.0 Reference Manual  /  ...  /  Server System Variables

5.1.8 Server System Variables

The MySQL server maintains many system variables that configure its operation. Each system variable has a default value. System variables can be set at server startup using options on the command line or in an option file. Most of them can be changed dynamically at runtime using the SET statement, which enables you to modify operation of the server without having to stop and restart it. You can also use system variable values in expressions.

Setting a global system variable runtime value normally requires the SYSTEM_VARIABLES_ADMIN privilege (or the deprecated SUPER privilege). Setting a session system runtime variable value normally requires no special privileges and can be done by any user, although there are exceptions. For more information, see Section 5.1.9.1, 鈥淪ystem Variable Privileges鈥?/a>

There are several ways to see the names and values of system variables:

This section provides a description of each system variable. For a system variable summary table, see Section 5.1.5, 鈥淪erver System Variable Reference鈥?/a>. For more information about manipulation of system variables, see Section 5.1.9, 鈥淯sing System Variables鈥?/a>.

For additional system variable information, see these sections:

Note

Some of the following variable descriptions refer to 鈥?span class="quote">enabling鈥?/span> or 鈥?span class="quote">disabling鈥?/span> a variable. These variables can be enabled with the SET statement by setting them to ON or 1, or disabled by setting them to OFF or 0. Boolean variables can be set at startup to the values ON, TRUE, OFF, and FALSE (not case-sensitive), as well as 1 and 0. See Section 4.2.2.4, 鈥淧rogram Option Modifiers鈥?/a>.

Some system variables control the size of buffers or caches. For a given buffer, the server might need to allocate internal data structures. These structures typically are allocated from the total memory allocated to the buffer, and the amount of space required might be platform dependent. This means that when you assign a value to a system variable that controls a buffer size, the amount of space actually available might differ from the value assigned. In some cases, the amount might be less than the value assigned. It is also possible that the server adjusts a value upward. For example, if you assign a value of 0 to a variable for which the minimal value is 1024, the server sets the value to 1024.

Values for buffer sizes, lengths, and stack sizes are given in bytes unless otherwise specified.

Some system variables take file name values. Unless otherwise specified, the default file location is the data directory if the value is a relative path name. To specify the location explicitly, use an absolute path name. Suppose that the data directory is /var/mysql/data. If a file-valued variable is given as a relative path name, it is located under /var/mysql/data. If the value is an absolute path name, its location is as given by the path name.

  • activate_all_roles_on_login

    Command-Line Format --activate-all-roles-on-login[={OFF|ON}]
    System Variable activate_all_roles_on_login
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Boolean
    Default Value OFF

    Whether to enable automatic activation of all granted roles when users log in to the server:

    Granted roles include those granted explicitly to the user and those named in the mandatory_roles system variable value.

    activate_all_roles_on_login applies only at login time, and at the beginning of execution for stored programs and views that execute in definer context. To change the active roles within a session, use SET ROLE. To change the active roles for a stored program, the program body should execute SET ROLE.

  • admin_address

    Command-Line Format --admin-address=addr
    Introduced 8.0.14
    System Variable admin_address
    Scope Global
    Dynamic No
    SET_VAR Hint Applies No
    Type String

    The IP address on which to listen for TCP/IP connections on the administrative network interface (see Section 5.1.12.1, 鈥淐onnection Interfaces鈥?/a>). There is no default admin_address value. If this variable is not specified at startup, the server maintains no administrative interface. The server also has a bind_address system variable for configuring regular (nonadministrative) client TCP/IP connections. See Section 5.1.12.1, 鈥淐onnection Interfaces鈥?/a>.

    If admin_address is specified, its value must satisfy these requirements:

    • The value must be a single IPv4 address, IPv6 address, or host name.

    • The value cannot specify a wildcard address format (*, 0.0.0.0, or ::).

    • As of MySQL 8.0.22, the value may include a network namespace specifier.

    An IP address can be specified as an IPv4 or IPv6 address. If the value is a host name, the server resolves the name to an IP address and binds to that address. If a host name resolves to multiple IP addresses, the server uses the first IPv4 address if there are any, or the first IPv6 address otherwise.

    The server treats different types of addresses as follows:

    • If the address is an IPv4-mapped address, the server accepts TCP/IP connections for that address, in either IPv4 or IPv6 format. For example, if the server is bound to ::ffff:127.0.0.1, clients can connect using --host=127.0.0.1 or --host=::ffff:127.0.0.1.

    • If the address is a 鈥?span class="quote">regular鈥?/span> IPv4 or IPv6 address (such as 127.0.0.1 or ::1), the server accepts TCP/IP connections only for that IPv4 or IPv6 address.

    These rules apply to specifying a network namespace for an address:

    • A network namespace can be specified for an IP address or a host name.

    • A network namespace cannot be specified for a wildcard IP address.

    • For a given address, the network namespace is optional. If given, it must be specified as a /ns suffix immediately following the address.

    • An address with no /ns suffix uses the host system global namespace. The global namespace is therefore the default.

    • An address with a /ns suffix uses the namespace named ns.

    • The host system must support network namespaces and each named namespace must previously have been set up. Naming a nonexistent namespace produces an error.

    For additional information about network namespaces, see Section 5.1.14, 鈥淣etwork Namespace Support鈥?/a>.

    If binding to the address fails, the server produces an error and does not start.

    The admin_address system variable is similar to the bind_address system variable that binds the server to an address for ordinary client connections, but with these differences:

  • admin_port

    Command-Line Format --admin-port=port_num
    Introduced 8.0.14
    System Variable admin_port
    Scope Global
    Dynamic No
    SET_VAR Hint Applies No
    Type Integer
    Default Value 33062
    Minimum Value 0
    Maximum Value 65535

    The TCP/IP port number to use for connections on the administrative network interface (see Section 5.1.12.1, 鈥淐onnection Interfaces鈥?/a>). Setting this variable to 0 causes the default value to be used.

    Setting admin_port has no effect if admin_address is not specified because in that case the server maintains no administrative network interface.

  • admin_ssl_ca

    Command-Line Format --admin-ssl-ca=file_name
    Introduced 8.0.21
    System Variable admin_ssl_ca
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type File name
    Default Value NULL

    The admin_ssl_ca system variable is like ssl_ca, except that it applies to the administrative connection interface rather than the main connection interface. For information about configuring encryption support for the administrative interface, see Administrative Interface Support for Encrypted Connections.

  • admin_ssl_capath

    Command-Line Format --admin-ssl-capath=dir_name
    Introduced 8.0.21
    System Variable admin_ssl_capath
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Directory name
    Default Value NULL

    The admin_ssl_capath system variable is like ssl_capath, except that it applies to the administrative connection interface rather than the main connection interface. For information about configuring encryption support for the administrative interface, see Administrative Interface Support for Encrypted Connections.

  • admin_ssl_cert

    Command-Line Format --admin-ssl-cert=file_name
    Introduced 8.0.21
    System Variable admin_ssl_cert
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type File name
    Default Value NULL

    The admin_ssl_cert system variable is like ssl_cert, except that it applies to the administrative connection interface rather than the main connection interface. For information about configuring encryption support for the administrative interface, see Administrative Interface Support for Encrypted Connections.

  • admin_ssl_cipher

    Command-Line Format --admin-ssl-cipher=name
    Introduced 8.0.21
    System Variable admin_ssl_cipher
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type String
    Default Value NULL

    The admin_ssl_cipher system variable is like ssl_cipher, except that it applies to the administrative connection interface rather than the main connection interface. For information about configuring encryption support for the administrative interface, see Administrative Interface Support for Encrypted Connections.

  • admin_ssl_crl

    Command-Line Format --admin-ssl-crl=file_name
    Introduced 8.0.21
    System Variable admin_ssl_crl
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type File name
    Default Value NULL

    The admin_ssl_crl system variable is like ssl_crl, except that it applies to the administrative connection interface rather than the main connection interface. For information about configuring encryption support for the administrative interface, see Administrative Interface Support for Encrypted Connections.

  • admin_ssl_crlpath

    Command-Line Format --admin-ssl-crlpath=dir_name
    Introduced 8.0.21
    System Variable admin_ssl_crlpath
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Directory name
    Default Value NULL

    The admin_ssl_crlpath system variable is like ssl_crlpath, except that it applies to the administrative connection interface rather than the main connection interface. For information about configuring encryption support for the administrative interface, see Administrative Interface Support for Encrypted Connections.

  • admin_ssl_key

    Command-Line Format --admin-ssl-key=file_name
    Introduced 8.0.21
    System Variable admin_ssl_key
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type File name
    Default Value NULL

    The admin_ssl_key system variable is like ssl_key, except that it applies to the administrative connection interface rather than the main connection interface. For information about configuring encryption support for the administrative interface, see Administrative Interface Support for Encrypted Connections.

  • admin_tls_ciphersuites

    Command-Line Format --admin-tls-ciphersuites=ciphersuite_list
    Introduced 8.0.21
    System Variable admin_tls_ciphersuites
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type String
    Default Value NULL

    The admin_tls_ciphersuites system variable is like tls_ciphersuites, except that it applies to the administrative connection interface rather than the main connection interface. For information about configuring encryption support for the administrative interface, see Administrative Interface Support for Encrypted Connections.

  • admin_tls_version

    Command-Line Format --admin-tls-version=protocol_list
    Introduced 8.0.21
    System Variable admin_tls_version
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type String
    Default Value (鈮?8.0.28) TLSv1.2,TLSv1.3
    Default Value (鈮?8.0.21, 鈮?8.0.27) TLSv1,TLSv1.1,TLSv1.2,TLSv1.3

    The admin_tls_version system variable is like tls_version, except that it applies to the administrative connection interface rather than the main connection interface. For information about configuring encryption support for the administrative interface, see Administrative Interface Support for Encrypted Connections.

    Important
    • Support for the TLSv1 and TLSv1.1 connection protocols is removed from MySQL Server as of MySQL 8.0.28. The protocols were deprecated from MySQL 8.0.26. See Removal of Support for the TLSv1 and TLSv1.1 Protocols for more information.

    • Support for the TLSv1.3 protocol is available in MySQL Server as of MySQL 8.0.16, provided that MySQL Server was compiled using OpenSSL 1.1.1 or higher. The server checks the version of OpenSSL at startup, and if it is lower than 1.1.1, TLSv1.3 is removed from the default value for the system variable. In that case, the defaults are 鈥?span class="quote">TLSv1,TLSv1.1,TLSv1.2鈥?/span> up to and including MySQL 8.0.27, and 鈥?span class="quote">TLSv1.2鈥?/span> from MySQL 8.0.28.

  • authentication_policy

    Command-Line Format --authentication-policy=value
    Introduced 8.0.27
    System Variable authentication_policy
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type String
    Default Value *,,

    This variable is used to administer multifactor authentication (MFA) capabilities. It applies to the authentication factor-related clauses of CREATE USER and ALTER USER statements used to manage MySQL account definitions, where 鈥?span class="quote">factor鈥?/span> corresponds to an authentication method or plugin associated with an account:

    Because authentication_policy applies only when accounts are created or altered, changes to its value have no effect on existing user accounts.

    Note

    Although the authentication_policy system variable places certain constraints on the authentication-related clauses of CREATE USER and ALTER USER statements, a user who has the AUTHENTICATION_POLICY_ADMIN privilege is not subject to the constraints. (A warning does occur for statements that otherwise would not be permitted.)

    The value of authentication_policy is a list of 1, 2, or 3 comma-separated elements. Each element present can be an authentication plugin name, an asterisk (*), empty, or missing. (Exception: Element 1 cannot be empty or missing.) In all cases, an element may be surrounded by whitespace characters and the entire list is enclosed in single quotes.

    The type of value specified for element N in the list has implications for whether factor N must be present in account definitions, and which authentication plugins can be used:

    • If element N is an authentication plugin name, an authentication method for factor N is required and must use the named plugin.

      In addition, the plugin becomes the default plugin for factor N authentication methods that do not name a plugin explicitly. For details, see The Default Authentication Plugin.

      Authentication plugins that use internal credentials storage can only be specified for the first element and cannot repeat. For example, the following settings are not permitted:

      • authenication_policy = 'caching_sha2_password, sha256_password'

      • authentication_policy = 'caching_sha2_password, authetication_fido, sha256_password'

    • If element N is an asterisk (*), an authentication method for factor N is required. It may use any authentication plugin that is valid for element N (as described later).

    • If element N is empty, an authentication method for factor N is optional. If given, it may use any authentication plugin that is valid for element N (as described later).

    • If element N is missing from the list (that is, there are fewer than N鈭? commas in the value), an authentication method for factor N is forbidden. For example, a value of '*' permits only a single factor and thus enforces single-factor authentication (1FA) for new accounts created with CREATE USER or changes to existing accounts made with ALTER USER. In this case, such statements cannot specify authentication for factors 2 or 3.

    When an authentication_policy element names an authentication plugin, the permitted plugin names for the element are subject to these conditions:

    • Element 1 must name a plugin that does not require a registration step. For example, authentication_fido cannot be named.

    • Elements 2 and 3 must name a plugin that does not use internal credentials storage.

      For information about which authentication plugins use internal credentials storage, see Section 6.2.15, 鈥淧assword Management鈥?/a>.

    When authentication_policy element N is *, the permitted plugin names for factor N in account definitions are subject to these conditions:

    • For factor 1, account definitions can use any plugin. Default authentication plugin rules apply for authentication specifications that do not name a plugin. See The Default Authentication Plugin.

    • For factors 2 and 3, account definitions cannot name a plugin that uses internal credentials storage. For example, with '*,*', '*,*,*', '*,', '*,,' authentication_policy settings, plugins that use internal credentials storage are only permitted for the first factor and cannot repeat.

    When authentication_policy element N is empty, the permitted plugin names for factor N in account definitions are subject to these conditions:

    • For factor 1, this does not apply because element 1 cannot be empty.

    • For factors 2 and 3, account definitions cannot name a plugin that uses internal credentials storage.

    Empty elements must occur at the end of the list, following a nonempty element. In other words, the first element cannot be empty, and either no element is empty or the last element is empty or the last two elements are empty. For example, a value of ',,' is not permitted because it would signify that all factors are optional. That cannot be; accounts must have at least one authentication factor.

    The default value of authentication_policy is '*,,'. This means that factor 1 is required in account definitions and can use any authentication plugin, and that factors 2 and 3 are optional and each can use any authentication plugin that does not use internal credentials storage.

    The following table shows some authentication_policy values and the policy that each establishes for creating or altering accounts.

    Table 5.4 Example authentication_policy Values

    authentication_policy Value Effective Policy
    '*' Permit only creating or altering accounts with one factor.
    '*,*' Permit only creating or altering accounts with two factors.
    '*,*,*' Permit only creating or altering accounts with three factors.
    '*,' Permit creating or altering accounts with one or two factors.
    '*,,' Permit creating or altering accounts with one, two, or three factors.
    '*,*,' Permit creating or altering accounts with two or three factors.
    '*,auth_plugin' Permit creating or altering accounts with two factors, where the first factor can be any authentication method, and the second factor must be the named plugin.
    'auth_plugin,*,' Permit creating or altering accounts with two or three factors, where the first factor must be the named plugin.
    'auth_plugin,' Permit creating or altering accounts with one or two factors, where the first factor must be the named plugin.
    'auth_plugin,auth_plugin,auth_plugin' Permits creating or altering accounts with three factors, where the factors must use the named plugins.
    authentication_policy Value Effective Policy

  • authentication_windows_log_level

    Command-Line Format --authentication-windows-log-level=#
    System Variable authentication_windows_log_level
    Scope Global
    Dynamic No
    SET_VAR Hint Applies No
    Type Integer
    Default Value 2
    Minimum Value 0
    Maximum Value 4

    This variable is available only if the authentication_windows Windows authentication plugin is enabled and debugging code is enabled. See Section 6.4.1.6, 鈥淲indows Pluggable Authentication鈥?/a>.

    This variable sets the logging level for the Windows authentication plugin. The following table shows the permitted values.

    Value Description
    0 No logging
    1 Log only error messages
    2 Log level 1 messages and warning messages
    3 Log level 2 messages and information notes
    4 Log level 3 messages and debug messages
  • authentication_windows_use_principal_name

    Command-Line Format --authentication-windows-use-principal-name[={OFF|ON}]
    System Variable authentication_windows_use_principal_name
    Scope Global
    Dynamic No
    SET_VAR Hint Applies No
    Type Boolean
    Default Value ON

    This variable is available only if the authentication_windows Windows authentication plugin is enabled. See Section 6.4.1.6, 鈥淲indows Pluggable Authentication鈥?/a>.

    A client that authenticates using the InitSecurityContext() function should provide a string identifying the service to which it connects (targetName). MySQL uses the principal name (UPN) of the account under which the server is running. The UPN has the form user_id@computer_name and need not be registered anywhere to be used. This UPN is sent by the server at the beginning of authentication handshake.

    This variable controls whether the server sends the UPN in the initial challenge. By default, the variable is enabled. For security reasons, it can be disabled to avoid sending the server's account name to a client as cleartext. If the variable is disabled, the server always sends a 0x00 byte in the first challenge, the client does not specify targetName, and as a result, NTLM authentication is used.

    If the server fails to obtain its UPN (which happens primarily in environments that do not support Kerberos authentication), the UPN is not sent by the server and NTLM authentication is used.

  • autocommit

    Command-Line Format --autocommit[={OFF|ON}]
    System Variable autocommit
    Scope Global, Session
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Boolean
    Default Value ON

    The autocommit mode. If set to 1, all changes to a table take effect immediately. If set to 0, you must use COMMIT to accept a transaction or ROLLBACK to cancel it. If autocommit is 0 and you change it to 1, MySQL performs an automatic COMMIT of any open transaction. Another way to begin a transaction is to use a START TRANSACTION or BEGIN statement. See Section 13.3.1, 鈥淪TART TRANSACTION, COMMIT, and ROLLBACK Statements鈥?/a>.

    By default, client connections begin with autocommit set to 1. To cause clients to begin with a default of 0, set the global autocommit value by starting the server with the --autocommit=0 option. To set the variable using an option file, include these lines:

    Press CTRL+C to copy
    [mysqld] autocommit=0
  • automatic_sp_privileges

    Command-Line Format --automatic-sp-privileges[={OFF|ON}]
    System Variable automatic_sp_privileges
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Boolean
    Default Value ON

    When this variable has a value of 1 (the default), the server automatically grants the EXECUTE and ALTER ROUTINE privileges to the creator of a stored routine, if the user cannot already execute and alter or drop the routine. (The ALTER ROUTINE privilege is required to drop the routine.) The server also automatically drops those privileges from the creator when the routine is dropped. If automatic_sp_privileges is 0, the server does not automatically add or drop these privileges.

    The creator of a routine is the account used to execute the CREATE statement for it. This might not be the same as the account named as the DEFINER in the routine definition.

    If you start mysqld with --skip-new, automatic_sp_privileges is set to OFF.

    See also Section 25.2.2, 鈥淪tored Routines and MySQL Privileges鈥?/a>.

  • auto_generate_certs

    Command-Line Format --auto-generate-certs[={OFF|ON}]
    System Variable auto_generate_certs
    Scope Global
    Dynamic No
    SET_VAR Hint Applies No
    Type Boolean
    Default Value ON

    This variable controls whether the server autogenerates SSL key and certificate files in the data directory, if they do not already exist.

    At startup, the server automatically generates server-side and client-side SSL certificate and key files in the data directory if the auto_generate_certs system variable is enabled, no SSL options other than --ssl are specified, and the server-side SSL files are missing from the data directory. These files enable secure client connections using SSL; see Section 6.3.1, 鈥淐onfiguring MySQL to Use Encrypted Connections鈥?/a>.

    For more information about SSL file autogeneration, including file names and characteristics, see Section 6.3.3.1, 鈥淐reating SSL and RSA Certificates and Keys using MySQL鈥?/a>

    The sha256_password_auto_generate_rsa_keys and caching_sha2_password_auto_generate_rsa_keys system variables are related but control autogeneration of RSA key-pair files needed for secure password exchange using RSA over unencrypted connections.

  • avoid_temporal_upgrade

    Command-Line Format --avoid-temporal-upgrade[={OFF|ON}]
    Deprecated Yes
    System Variable avoid_temporal_upgrade
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Boolean
    Default Value OFF

    This variable controls whether ALTER TABLE implicitly upgrades temporal columns found to be in pre-5.6.4 format (TIME, DATETIME, and TIMESTAMP columns without support for fractional seconds precision). Upgrading such columns requires a table rebuild, which prevents any use of fast alterations that might otherwise apply to the operation to be performed.

    This variable is disabled by default. Enabling it causes ALTER TABLE not to rebuild temporal columns and thereby be able to take advantage of possible fast alterations.

    This variable is deprecated; expect it to be removed in a future MySQL release.

  • back_log

    Command-Line Format --back-log=#
    System Variable back_log
    Scope Global
    Dynamic No
    SET_VAR Hint Applies No
    Type Integer
    Default Value -1 (signifies autosizing; do not assign this literal value)
    Minimum Value 1
    Maximum Value 65535

    The number of outstanding connection requests MySQL can have. This comes into play when the main MySQL thread gets very many connection requests in a very short time. It then takes some time (although very little) for the main thread to check the connection and start a new thread. The back_log value indicates how many requests can be stacked during this short time before MySQL momentarily stops answering new requests. You need to increase this only if you expect a large number of connections in a short period of time.

    In other words, this value is the size of the listen queue for incoming TCP/IP connections. Your operating system has its own limit on the size of this queue. The manual page for the Unix listen() system call should have more details. Check your OS documentation for the maximum value for this variable. back_log cannot be set higher than your operating system limit.

    The default value is the value of max_connections, which enables the permitted backlog to adjust to the maximum permitted number of connections.

  • basedir

    Command-Line Format --basedir=dir_name
    System Variable basedir
    Scope Global
    Dynamic No
    SET_VAR Hint Applies No
    Type Directory name
    Default Value parent of mysqld installation directory

    The path to the MySQL installation base directory.

  • big_tables

    Command-Line Format --big-tables[={OFF|ON}]
    System Variable big_tables
    Scope Global, Session
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Boolean
    Default Value OFF

    If enabled, the server stores all temporary tables on disk rather than in memory. This prevents most The table tbl_name is full errors for SELECT operations that require a large temporary table, but also slows down queries for which in-memory tables would suffice.

    The default value for new connections is OFF (use in-memory temporary tables). Normally, it should never be necessary to enable this variable. When in-memory internal temporary tables are managed by the TempTable storage engine (the default), and the maximum amount of memory that can be occupied by the TempTable storage engine is exceeded, the TempTable storage engine starts storing data to temporary files on disk. When in-memory temporary tables are managed by the MEMORY storage engine, in-memory tables are automatically converted to disk-based tables as required. For more information, see Section 8.4.4, 鈥淚nternal Temporary Table Use in MySQL鈥?/a>.

  • bind_address

    Command-Line Format --bind-address=addr
    System Variable bind_address
    Scope Global
    Dynamic No
    SET_VAR Hint Applies No
    Type String
    Default Value *

    The MySQL server listens on one or more network sockets for TCP/IP connections. Each socket is bound to one address, but it is possible for an address to map onto multiple network interfaces. To specify how the server should listen for TCP/IP connections, set the bind_address system variable at server startup. The server also has an admin_address system variable that enables administrative connections on a dedicated interface. See Section 5.1.12.1, 鈥淐onnection Interfaces鈥?/a>.

    If bind_address is specified, its value must satisfy these requirements:

    • Prior to MySQL 8.0.13, bind_address accepts a single address value, which may specify a single non-wildcard IP address or host name, or one of the wildcard address formats that permit listening on multiple network interfaces (*, 0.0.0.0, or ::).

    • As of MySQL 8.0.13, bind_address accepts either a single value as just described, or a list of comma-separated values. When the variable names a list of multiple values, each value must specify a single non-wildcard IP address (either IPv4 or IPv6) or a host name. Wildcard address formats (*, 0.0.0.0, or ::) are not allowed in a list of values.

    • As of MySQL 8.0.22, addresses may include a network namespace specifier.

    IP addresses can be specified as IPv4 or IPv6 addresses. For any value that is a host name, the server resolves the name to an IP address and binds to that address. If a host name resolves to multiple IP addresses, the server uses the first IPv4 address if there are any, or the first IPv6 address otherwise.

    The server treats different types of addresses as follows:

    • If the address is *, the server accepts TCP/IP connections on all server host IPv4 interfaces, and, if the server host supports IPv6, on all IPv6 interfaces. Use this address to permit both IPv4 and IPv6 connections on all server interfaces. This value is the default. If the variable specifies a list of multiple values, this value is not permitted.

    • If the address is 0.0.0.0, the server accepts TCP/IP connections on all server host IPv4 interfaces. If the variable specifies a list of multiple values, this value is not permitted.

    • If the address is ::, the server accepts TCP/IP connections on all server host IPv4 and IPv6 interfaces. If the variable specifies a list of multiple values, this value is not permitted.

    • If the address is an IPv4-mapped address, the server accepts TCP/IP connections for that address, in either IPv4 or IPv6 format. For example, if the server is bound to ::ffff:127.0.0.1, clients can connect using --host=127.0.0.1 or --host=::ffff:127.0.0.1.

    • If the address is a 鈥?span class="quote">regular鈥?/span> IPv4 or IPv6 address (such as 127.0.0.1 or ::1), the server accepts TCP/IP connections only for that IPv4 or IPv6 address.

    These rules apply to specifying a network namespace for an address:

    • A network namespace can be specified for an IP address or a host name.

    • A network namespace cannot be specified for a wildcard IP address.

    • For a given address, the network namespace is optional. If given, it must be specified as a /ns suffix immediately following the address.

    • An address with no /ns suffix uses the host system global namespace. The global namespace is therefore the default.

    • An address with a /ns suffix uses the namespace named ns.

    • The host system must support network namespaces and each named namespace must previously have been set up. Naming a nonexistent namespace produces an error.

    • If the variable value specifies multiple addresses, it can include addresses in the global namespace, in named namespaces, or a mix.

    For additional information about network namespaces, see Section 5.1.14, 鈥淣etwork Namespace Support鈥?/a>.

    If binding to any address fails, the server produces an error and does not start.

    Examples:

    When bind_address names a single value (wildcard or non-wildcard), the server listens on a single socket, which for a wildcard address may be bound to multiple network interfaces. When bind_address names a list of multiple values, the server listens on one socket per value, with each socket bound to a single network interface. The number of sockets is linear with the number of values specified. Depending on operating system connection-acceptance efficiency, long value lists might incur a performance penalty for accepting TCP/IP connections.

    Because file descriptors are allocated for listening sockets and network namespace files, it may be necessary to increase the open_files_limit system variable.

    If you intend to bind the server to a specific address, be sure that the mysql.user system table contains an account with administrative privileges that you can use to connect to that address. Otherwise, you cannot shut down the server. For example, if you bind the server to *, you can connect to it using all existing accounts. But if you bind the server to ::1, it accepts connections only on that address. In that case, first make sure that the 'root'@'::1' account is present in the mysql.user table so you can still connect to the server to shut it down.

  • block_encryption_mode

    Command-Line Format --block-encryption-mode=#
    System Variable block_encryption_mode
    Scope Global, Session
    Dynamic Yes
    SET_VAR Hint Applies No
    Type String
    Default Value aes-128-ecb

    This variable controls the block encryption mode for block-based algorithms such as AES. It affects encryption for AES_ENCRYPT() and AES_DECRYPT().

    block_encryption_mode takes a value in aes-keylen-mode format, where keylen is the key length in bits and mode is the encryption mode. The value is not case-sensitive. Permitted keylen values are 128, 192, and 256. Permitted mode values are ECB, CBC, CFB1, CFB8, CFB128, and OFB.

    For example, this statement causes the AES encryption functions to use a key length of 256 bits and the CBC mode:

    Press CTRL+C to copy
    SET block_encryption_mode = 'aes-256-cbc';

    An error occurs for attempts to set block_encryption_mode to a value containing an unsupported key length or a mode that the SSL library does not support.

  • build_id

    Introduced 8.0.31
    System Variable build_id
    Scope Global
    Dynamic No
    SET_VAR Hint Applies No
    Platform Specific Linux

    This is a 160-bit SHA1 signature which is generated by the linker when compiling the server on Linux systems with -DWITH_BUILD_ID=ON (enabled by default), and converted to a hexadecimal string. This read-only value serves as a unique build ID, and is written into the server log at startup.

    build_id is not supported on platforms other than Linux.

  • bulk_insert_buffer_size

    Command-Line Format --bulk-insert-buffer-size=#
    System Variable bulk_insert_buffer_size
    Scope Global, Session
    Dynamic Yes
    SET_VAR Hint Applies Yes
    Type Integer
    Default Value 8388608
    Minimum Value 0
    Maximum Value (64-bit platforms) 18446744073709551615
    Maximum Value (32-bit platforms) 4294967295
    Unit bytes/thread

    MyISAM uses a special tree-like cache to make bulk inserts faster for INSERT ... SELECT, INSERT ... VALUES (...), (...), ..., and LOAD DATA when adding data to nonempty tables. This variable limits the size of the cache tree in bytes per thread. Setting it to 0 disables this optimization. The default value is 8MB.

    As of MySQL 8.0.14, setting the session value of this system variable is a restricted operation. The session user must have privileges sufficient to set restricted session variables. See Section 5.1.9.1, 鈥淪ystem Variable Privileges鈥?/a>.

  • caching_sha2_password_digest_rounds

    Command-Line Format --caching-sha2-password-digest-rounds=#
    Introduced 8.0.24
    System Variable caching_sha2_password_digest_rounds
    Scope Global
    Dynamic No
    SET_VAR Hint Applies No
    Type Integer
    Default Value 5000
    Minimum Value 5000
    Maximum Value 4095000

    The number of hash rounds used by the caching_sha2_password authentication plugin for password storage.

    Increasing the number of hashing rounds above the default value incurs a performance penalty that correlates with the amount of increase:

    • Creating an account that uses the caching_sha2_password plugin has no impact on the client session within which the account is created, but the server must perform the hashing rounds to complete the operation.

    • For client connections that use the account, the server must perform the hashing rounds and save the result in the cache. The result is longer login time for the first client connection, but not for subsequent connections. This behavior occurs after each server restart.

  • caching_sha2_password_auto_generate_rsa_keys

    Command-Line Format --caching-sha2-password-auto-generate-rsa-keys[={OFF|ON}]
    System Variable caching_sha2_password_auto_generate_rsa_keys
    Scope Global
    Dynamic No
    SET_VAR Hint Applies No
    Type Boolean
    Default Value ON

    The server uses this variable to determine whether to autogenerate RSA private/public key-pair files in the data directory if they do not already exist.

    At startup, the server automatically generates RSA private/public key-pair files in the data directory if all of these conditions are true: The sha256_password_auto_generate_rsa_keys or caching_sha2_password_auto_generate_rsa_keys system variable is enabled; no RSA options are specified; the RSA files are missing from the data directory. These key-pair files enable secure password exchange using RSA over unencrypted connections for accounts authenticated by the sha256_password or caching_sha2_password plugin; see Section 6.4.1.3, 鈥淪HA-256 Pluggable Authentication鈥?/a>, and Section 6.4.1.2, 鈥淐aching SHA-2 Pluggable Authentication鈥?/a>.

    For more information about RSA file autogeneration, including file names and characteristics, see Section 6.3.3.1, 鈥淐reating SSL and RSA Certificates and Keys using MySQL鈥?/a>

    The auto_generate_certs system variable is related but controls autogeneration of SSL certificate and key files needed for secure connections using SSL.

  • caching_sha2_password_private_key_path

    Command-Line Format --caching-sha2-password-private-key-path=file_name
    System Variable caching_sha2_password_private_key_path
    Scope Global
    Dynamic No
    SET_VAR Hint Applies No
    Type File name
    Default Value private_key.pem

    This variable specifies the path name of the RSA private key file for the caching_sha2_password authentication plugin. If the file is named as a relative path, it is interpreted relative to the server data directory. The file must be in PEM format.

    Important

    Because this file stores a private key, its access mode should be restricted so that only the MySQL server can read it.

    For information about caching_sha2_password, see Section 6.4.1.2, 鈥淐aching SHA-2 Pluggable Authentication鈥?/a>.

  • caching_sha2_password_public_key_path

    Command-Line Format --caching-sha2-password-public-key-path=file_name
    System Variable caching_sha2_password_public_key_path
    Scope Global
    Dynamic No
    SET_VAR Hint Applies No
    Type File name
    Default Value public_key.pem

    This variable specifies the path name of the RSA public key file for the caching_sha2_password authentication plugin. If the file is named as a relative path, it is interpreted relative to the server data directory. The file must be in PEM format.

    For information about caching_sha2_password, including information about how clients request the RSA public key, see Section 6.4.1.2, 鈥淐aching SHA-2 Pluggable Authentication鈥?/a>.

  • character_set_client

    System Variable character_set_client
    Scope Global, Session
    Dynamic Yes
    SET_VAR Hint Applies No
    Type String
    Default Value utf8mb4

    The character set for statements that arrive from the client. The session value of this variable is set using the character set requested by the client when the client connects to the server. (Many clients support a --default-character-set option to enable this character set to be specified explicitly. See also Section 10.4, 鈥淐onnection Character Sets and Collations鈥?/a>.) The global value of the variable is used to set the session value in cases when the client-requested value is unknown or not available, or the server is configured to ignore client requests:

    Some character sets cannot be used as the client character set. Attempting to use them as the character_set_client value produces an error. See Impermissible Client Character Sets.

  • character_set_connection

    System Variable character_set_connection
    Scope Global, Session
    Dynamic Yes
    SET_VAR Hint Applies No
    Type String
    Default Value utf8mb4

    The character set used for literals specified without a character set introducer and for number-to-string conversion. For information about introducers, see Section 10.3.8, 鈥淐haracter Set Introducers鈥?/a>.

  • character_set_database

    System Variable character_set_database
    Scope Global, Session
    Dynamic Yes
    SET_VAR Hint Applies No
    Type String
    Default Value utf8mb4
    Footnote This option is dynamic, but should be set only by server. You should not set this variable manually.

    The character set used by the default database. The server sets this variable whenever the default database changes. If there is no default database, the variable has the same value as character_set_server.

    As of MySQL 8.0.14, setting the session value of this system variable is a restricted operation. The session user must have privileges sufficient to set restricted session variables. See Section 5.1.9.1, 鈥淪ystem Variable Privileges鈥?/a>.

    The global character_set_database and collation_database system variables are deprecated; expect them to be removed in a future version of MySQL.

    Assigning a value to the session character_set_database and collation_database system variables is deprecated and assignments produce a warning. Expect the session variables to become read-only (and assignments to them to produce an error) in a future version of MySQL in which it remains possible to access the session variables to determine the database character set and collation for the default database.

  • character_set_filesystem

    Command-Line Format --character-set-filesystem=name
    System Variable character_set_filesystem
    Scope Global, Session
    Dynamic Yes
    SET_VAR Hint Applies No
    Type String
    Default Value binary

    The file system character set. This variable is used to interpret string literals that refer to file names, such as in the LOAD DATA and SELECT ... INTO OUTFILE statements and the LOAD_FILE() function. Such file names are converted from character_set_client to character_set_filesystem before the file opening attempt occurs. The default value is binary, which means that no conversion occurs. For systems on which multibyte file names are permitted, a different value may be more appropriate. For example, if the system represents file names using UTF-8, set character_set_filesystem to 'utf8mb4'.

    As of MySQL 8.0.14, setting the session value of this system variable is a restricted operation. The session user must have privileges sufficient to set restricted session variables. See Section 5.1.9.1, 鈥淪ystem Variable Privileges鈥?/a>.

  • character_set_results

    System Variable character_set_results
    Scope Global, Session
    Dynamic Yes
    SET_VAR Hint Applies No
    Type String
    Default Value utf8mb4

    The character set used for returning query results to the client. This includes result data such as column values, result metadata such as column names, and error messages.

  • character_set_server

    Command-Line Format --character-set-server=name
    System Variable character_set_server
    Scope Global, Session
    Dynamic Yes
    SET_VAR Hint Applies No
    Type String
    Default Value utf8mb4

    The servers default character set. See Section 10.15, 鈥淐haracter Set Configuration鈥?/a>. If you set this variable, you should also set collation_server to specify the collation for the character set.

  • character_set_system

    System Variable character_set_system
    Scope Global
    Dynamic No
    SET_VAR Hint Applies No
    Type String
    Default Value utf8mb3

    The character set used by the server for storing identifiers. The value is always utf8mb3.

  • character_sets_dir

    Command-Line Format --character-sets-dir=dir_name
    System Variable character_sets_dir
    Scope Global
    Dynamic No
    SET_VAR Hint Applies No
    Type Directory name

    The directory where character sets are installed. See Section 10.15, 鈥淐haracter Set Configuration鈥?/a>.

  • check_proxy_users

    Command-Line Format --check-proxy-users[={OFF|ON}]
    System Variable check_proxy_users
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Boolean
    Default Value OFF

    Some authentication plugins implement proxy user mapping for themselves (for example, the PAM and Windows authentication plugins). Other authentication plugins do not support proxy users by default. Of these, some can request that the MySQL server itself map proxy users according to granted proxy privileges: mysql_native_password, sha256_password.

    If the check_proxy_users system variable is enabled, the server performs proxy user mapping for any authentication plugins that make such a request. However, it may also be necessary to enable plugin-specific system variables to take advantage of server proxy user mapping support:

    For information about user proxying, see Section 6.2.19, 鈥淧roxy Users鈥?/a>.

  • collation_connection

    System Variable collation_connection
    Scope Global, Session
    Dynamic Yes
    SET_VAR Hint Applies No
    Type String

    The collation of the connection character set. collation_connection is important for comparisons of literal strings. For comparisons of strings with column values, collation_connection does not matter because columns have their own collation, which has a higher collation precedence (see Section 10.8.4, 鈥淐ollation Coercibility in Expressions鈥?/a>).

    In MySQL 8.0.33 and later, using the name of a user-defined collation for this variable raises a warning.

  • collation_database

    System Variable collation_database
    Scope Global, Session
    Dynamic Yes
    SET_VAR Hint Applies No
    Type String
    Default Value utf8mb4_0900_ai_ci
    Footnote This option is dynamic, but should be set only by server. You should not set this variable manually.

    The collation used by the default database. The server sets this variable whenever the default database changes. If there is no default database, the variable has the same value as collation_server.

    As of MySQL 8.0.18, setting the session value of this system variable is no longer a restricted operation.

    The global character_set_database and collation_database system variables are deprecated; expect them to be removed in a future version of MySQL.

    Assigning a value to the session character_set_database and collation_database system variables is deprecated and assignments produce a warning. Expect the session variables to become read-only (and assignments to produce an error) in a future version of MySQL in which it remains possible to access the session variables to determine the database character set and collation for the default database.

    In MySQL 8.0.33 and later, using the name of a user-defined collation for collation_database raises a warning.

  • collation_server

    Command-Line Format --collation-server=name
    System Variable collation_server
    Scope Global, Session
    Dynamic Yes
    SET_VAR Hint Applies No
    Type String
    Default Value utf8mb4_0900_ai_ci

    The server's default collation. See Section 10.15, 鈥淐haracter Set Configuration鈥?/a>.

    Beginning with MySQL 8.0.33, setting this to the name of a user-defined collation raises a warning.

  • completion_type

    Command-Line Format --completion-type=#
    System Variable completion_type
    Scope Global, Session
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Enumeration
    Default Value NO_CHAIN
    Valid Values

    NO_CHAIN

    CHAIN

    RELEASE

    0

    1

    2

    The transaction completion type. This variable can take the values shown in the following table. The variable can be assigned using either the name values or corresponding integer values.

    Value Description
    NO_CHAIN (or 0) COMMIT and ROLLBACK are unaffected. This is the default value.
    CHAIN (or 1) COMMIT and ROLLBACK are equivalent to COMMIT AND CHAIN and ROLLBACK AND CHAIN, respectively. (A new transaction starts immediately with the same isolation level as the just-terminated transaction.)
    RELEASE (or 2) COMMIT and ROLLBACK are equivalent to COMMIT RELEASE and ROLLBACK RELEASE, respectively. (The server disconnects after terminating the transaction.)

    completion_type affects transactions that begin with START TRANSACTION or BEGIN and end with COMMIT or ROLLBACK. It does not apply to implicit commits resulting from execution of the statements listed in Section 13.3.3, 鈥淪tatements That Cause an Implicit Commit鈥?/a>. It also does not apply for XA COMMIT, XA ROLLBACK, or when autocommit=1.

  • concurrent_insert

    Command-Line Format --concurrent-insert[=value]
    System Variable concurrent_insert
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Enumeration
    Default Value AUTO
    Valid Values

    NEVER

    AUTO

    ALWAYS

    0

    1

    2

    If AUTO (the default), MySQL permits INSERT and SELECT statements to run concurrently for MyISAM tables that have no free blocks in the middle of the data file.

    This variable can take the values shown in the following table. The variable can be assigned using either the name values or corresponding integer values.

    Value Description
    NEVER (or 0) Disables concurrent inserts
    AUTO (or 1) (Default) Enables concurrent insert for MyISAM tables that do not have holes
    ALWAYS (or 2) Enables concurrent inserts for all MyISAM tables, even those that have holes. For a table with a hole, new rows are inserted at the end of the table if it is in use by another thread. Otherwise, MySQL acquires a normal write lock and inserts the row into the hole.

    If you start mysqld with --skip-new, concurrent_insert is set to NEVER.

    See also Section 8.11.3, 鈥淐oncurrent Inserts鈥?/a>.

  • connect_timeout

    Command-Line Format --connect-timeout=#
    System Variable connect_timeout
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Integer
    Default Value 10
    Minimum Value 2
    Maximum Value 31536000
    Unit seconds

    The number of seconds that the mysqld server waits for a connect packet before responding with Bad handshake. The default value is 10 seconds.

    Increasing the connect_timeout value might help if clients frequently encounter errors of the form Lost connection to MySQL server at 'XXX', system error: errno.

  • connection_memory_chunk_size

    Command-Line Format --connection-memory-chunk-size=#
    Introduced 8.0.28
    System Variable connection_memory_chunk_size
    Scope Global, Session
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Integer
    Default Value 8912
    Minimum Value 0
    Maximum Value 536870912
    Unit bytes

    Set the chunking size for updates to the global memory usage counter Global_connection_memory. The status variable is updated only when total memory consumption by all user connections changes by more than this amount. Disable updates by setting connection_memory_chunk_size = 0.

    The memory calculation is exclusive of any memory used by system users such as the MySQL root user. Memory used by the InnoDB buffer pool is also not included.

    You must have the SYSTEM_VARIABLES_ADMIN or SUPER privilege to set this variable.

  • connection_memory_limit

    Command-Line Format --connection-memory-limit=#
    Introduced 8.0.28
    System Variable connection_memory_limit
    Scope Global, Session
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Integer
    Default Value 18446744073709551615
    Minimum Value 2097152
    Maximum Value 18446744073709551615
    Unit bytes

    Set the maximum amount of memory that can be used by a single user connection. If any user connection uses more than this amount, any new queries from this connection are rejected with ER_CONN_LIMIT.

    The limit set by this variable does not apply to system users, or to the MySQL root account. Memory used by the InnoDB buffer pool is also not included.

    You must have the SYSTEM_VARIABLES_ADMIN or SUPER privilege to set this variable.

  • core_file

    System Variable core_file
    Scope Global
    Dynamic No
    SET_VAR Hint Applies No
    Type Boolean
    Default Value OFF

    Whether to write a core file if the server unexpectedly exits. This variable is set by the --core-file option.

  • create_admin_listener_thread

    Command-Line Format --create-admin-listener-thread[={OFF|ON}]
    Introduced 8.0.14
    System Variable create_admin_listener_thread
    Scope Global
    Dynamic No
    SET_VAR Hint Applies No
    Type Boolean
    Default Value OFF

    Whether to use a dedicated listening thread for client connections on the administrative network interface (see Section 5.1.12.1, 鈥淐onnection Interfaces鈥?/a>). The default is OFF; that is, the manager thread for ordinary connections on the main interface also handles connections for the administrative interface.

    Depending on factors such as platform type and workload, you may find one setting for this variable yields better performance than the other setting.

    Setting create_admin_listener_thread has no effect if admin_address is not specified because in that case the server maintains no administrative network interface.

  • cte_max_recursion_depth

    Command-Line Format --cte-max-recursion-depth=#
    System Variable cte_max_recursion_depth
    Scope Global, Session
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Integer
    Default Value 1000
    Minimum Value 0
    Maximum Value 4294967295

    The common table expression (CTE) maximum recursion depth. The server terminates execution of any CTE that recurses more levels than the value of this variable. For more information, see Limiting Common Table Expression Recursion.

  • datadir

    Command-Line Format --datadir=dir_name
    System Variable datadir
    Scope Global
    Dynamic No
    SET_VAR Hint Applies No
    Type Directory name

    The path to the MySQL server data directory. Relative paths are resolved with respect to the current directory. If you expect the server to be started automatically (that is, in contexts for which you cannot know the current directory in advance), it is best to specify the datadir value as an absolute path.

  • debug

    Command-Line Format --debug[=debug_options]
    System Variable debug
    Scope Global, Session
    Dynamic Yes
    SET_VAR Hint Applies No
    Type String
    Default Value (Unix) d:t:i:o,/tmp/mysqld.trace
    Default Value (Windows) d:t:i:O,\mysqld.trace

    This variable indicates the current debugging settings. It is available only for servers built with debugging support. The initial value comes from the value of instances of the --debug option given at server startup. The global and session values may be set at runtime.

    Setting the session value of this system variable is a restricted operation. The session user must have privileges sufficient to set restricted session variables. See Section 5.1.9.1, 鈥淪ystem Variable Privileges鈥?/a>.

    Assigning a value that begins with + or - cause the value to added to or subtracted from the current value:

    For more information, see Section 5.9.4, 鈥淭he DBUG Package鈥?/a>.

  • debug_sync

    System Variable debug_sync
    Scope Session
    Dynamic Yes
    SET_VAR Hint Applies No
    Type String

    This variable is the user interface to the Debug Sync facility. Use of Debug Sync requires that MySQL be configured with the -DENABLE_DEBUG_SYNC=1 CMake option (see Section 2.9.7, 鈥淢ySQL Source-Configuration Options鈥?/a>). If Debug Sync is not compiled in, this system variable is not available.

    The global variable value is read only and indicates whether the facility is enabled. By default, Debug Sync is disabled and the value of debug_sync is OFF. If the server is started with --debug-sync-timeout=N, where N is a timeout value greater than 0, Debug Sync is enabled and the value of debug_sync is ON - current signal followed by the signal name. Also, N becomes the default timeout for individual synchronization points.

    The session value can be read by any user and has the same value as the global variable. The session value can be set to control synchronization points.

    Setting the session value of this system variable is a restricted operation. The session user must have privileges sufficient to set restricted session variables. See Section 5.1.9.1, 鈥淪ystem Variable Privileges鈥?/a>.

    For a description of the Debug Sync facility and how to use synchronization points, see MySQL Internals: Test Synchronization.

  • default_authentication_plugin

    Command-Line Format --default-authentication-plugin=plugin_name
    Deprecated 8.0.27
    System Variable default_authentication_plugin
    Scope Global
    Dynamic No
    SET_VAR Hint Applies No
    Type Enumeration
    Default Value caching_sha2_password
    Valid Values

    mysql_native_password

    sha256_password

    caching_sha2_password

    The default authentication plugin. This must be a plugin that uses internal credentials storage, so these values are permitted:

    For information about which authentication plugins use internal credentials storage, see Section 6.2.15, 鈥淧assword Management鈥?/a>.

    Prior to MySQL 8.0.27, the default_authentication_plugin value affects these aspects of server operation:

    • It determines which authentication plugin the server assigns to new accounts created by CREATE USER statements that do not explicitly specify an authentication plugin.

    • For an account created with a statement of the following form, the server associates the account with the default authentication plugin and assigns the account the given password, hashed as required by that plugin:

      Press CTRL+C to copy
      CREATE USER ... IDENTIFIED BY 'cleartext password';

    As of MySQL 8.0.27, which introduces multifactor authentication, default_authentication_plugin is still used, but in conjunction with and at a lower precedence than the authentication_policy system variable. For details, see The Default Authentication Plugin. Because of this diminished role, default_authentication_plugin is deprecated as of MySQL 8.0.27 and subject to removal in a future MySQL version.

  • default_collation_for_utf8mb4

    System Variable default_collation_for_utf8mb4
    Scope Global, Session
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Enumeration
    Valid Values

    utf8mb4_0900_ai_ci

    utf8mb4_general_ci

    Important

    The default_collation_for_utf8mb4 system variable is for for internal use by MySQL Replication only.

    This variable is set by the server to the default collation for the utf8mb4 character set. The value of the variable is replicated from a source to a replica so that the replica can correctly process data originating from a source with a different default collation for utf8mb4. This variable is primarily intended to support replication from a MySQL 5.7 or older replication source server to a MySQL 8.0 replica server, or group replication with a MySQL 5.7 primary node and one or more MySQL 8.0 secondaries. The default collation for utf8mb4 in MySQL 5.7 is utf8mb4_general_ci, but utf8mb4_0900_ai_ci in MySQL 8.0. The variable is not present in releases earlier than MySQL 8.0, so if the replica does not receive a value for the variable, it assumes the source is from an earlier release and sets the value to the previous default collation utf8mb4_general_ci.

    As of MySQL 8.0.18, setting the session value of this system variable is no longer a restricted operation.

    The default utf8mb4 collation is used in the following statements:

    See also Section 10.9, 鈥淯nicode Support鈥?/a>.

  • default_password_lifetime

    Command-Line Format --default-password-lifetime=#
    System Variable default_password_lifetime
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Integer
    Default Value 0
    Minimum Value 0
    Maximum Value 65535
    Unit days

    This variable defines the global automatic password expiration policy. The default default_password_lifetime value is 0, which disables automatic password expiration. If the value of default_password_lifetime is a positive integer N, it indicates the permitted password lifetime; passwords must be changed every N days.

    The global password expiration policy can be overridden as desired for individual accounts using the password expiration option of the CREATE USER and ALTER USER statements. See Section 6.2.15, 鈥淧assword Management鈥?/a>.

  • default_storage_engine

    Command-Line Format --default-storage-engine=name
    System Variable default_storage_engine
    Scope Global, Session
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Enumeration
    Default Value InnoDB

    The default storage engine for tables. See Chapter 16, Alternative Storage Engines. This variable sets the storage engine for permanent tables only. To set the storage engine for TEMPORARY tables, set the default_tmp_storage_engine system variable.

    To see which storage engines are available and enabled, use the SHOW ENGINES statement or query the INFORMATION_SCHEMA ENGINES table.

    If you disable the default storage engine at server startup, you must set the default engine for both permanent and TEMPORARY tables to a different engine, or else the server does not start.

  • default_table_encryption

    Command-Line Format --default-table-encryption[={OFF|ON}]
    Introduced 8.0.16
    System Variable default_table_encryption
    Scope Global, Session
    Dynamic Yes
    SET_VAR Hint Applies Yes
    Type Boolean
    Default Value OFF

    Defines the default encryption setting applied to schemas and general tablespaces when they are created without specifying an ENCRYPTION clause.

    The default_table_encryption variable is only applicable to user-created schemas and general tablespaces. It does not govern encryption of the mysql system tablespace.

    Setting the runtime value of default_table_encryption requires the SYSTEM_VARIABLES_ADMIN and TABLE_ENCRYPTION_ADMIN privileges, or the deprecated SUPER privilege.

    default_table_encryption supports SET PERSIST and SET PERSIST_ONLY syntax. See Section 5.1.9.3, 鈥淧ersisted System Variables鈥?/a>.

    For more information, see Defining an Encryption Default for Schemas and General Tablespaces.

  • default_tmp_storage_engine

    Command-Line Format --default-tmp-storage-engine=name
    System Variable default_tmp_storage_engine
    Scope Global, Session
    Dynamic Yes
    SET_VAR Hint Applies Yes
    Type Enumeration
    Default Value InnoDB

    The default storage engine for TEMPORARY tables (created with CREATE TEMPORARY TABLE). To set the storage engine for permanent tables, set the default_storage_engine system variable. Also see the discussion of that variable regarding possible values.

    If you disable the default storage engine at server startup, you must set the default engine for both permanent and TEMPORARY tables to a different engine, or else the server does not start.

  • default_week_format

    Command-Line Format --default-week-format=#
    System Variable default_week_format
    Scope Global, Session
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Integer
    Default Value 0
    Minimum Value 0
    Maximum Value 7

    The default mode value to use for the WEEK() function. See Section 12.7, 鈥淒ate and Time Functions鈥?/a>.

  • delay_key_write

    Command-Line Format --delay-key-write[={OFF|ON|ALL}]
    System Variable delay_key_write
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Enumeration
    Default Value ON
    Valid Values

    OFF

    ON

    ALL

    This variable specifies how to use delayed key writes. It applies only to MyISAM tables. Delayed key writing causes key buffers not to be flushed between writes. See also Section 16.2.1, 鈥淢yISAM Startup Options鈥?/a>.

    This variable can have one of the following values to affect handling of the DELAY_KEY_WRITE table option that can be used in CREATE TABLE statements.

    Option Description
    OFF DELAY_KEY_WRITE is ignored.
    ON MySQL honors any DELAY_KEY_WRITE option specified in CREATE TABLE statements. This is the default value.
    ALL All new opened tables are treated as if they were created with the DELAY_KEY_WRITE option enabled.
    Note

    If you set this variable to ALL, you should not use MyISAM tables from within another program (such as another MySQL server or myisamchk) when the tables are in use. Doing so leads to index corruption.

    If DELAY_KEY_WRITE is enabled for a table, the key buffer is not flushed for the table on every index update, but only when the table is closed. This speeds up writes on keys a lot, but if you use this feature, you should add automatic checking of all MyISAM tables by starting the server with the myisam_recover_options system variable set (for example, myisam_recover_options='BACKUP,FORCE'). See Section 5.1.8, 鈥淪erver System Variables鈥?/a>, and Section 16.2.1, 鈥淢yISAM Startup Options鈥?/a>.

    If you start mysqld with --skip-new, delay_key_write is set to OFF.

    Warning

    If you enable external locking with --external-locking, there is no protection against index corruption for tables that use delayed key writes.

  • delayed_insert_limit

    Command-Line Format --delayed-insert-limit=#
    Deprecated Yes
    System Variable delayed_insert_limit
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Integer
    Default Value 100
    Minimum Value 1
    Maximum Value (64-bit platforms) 18446744073709551615
    Maximum Value (32-bit platforms) 4294967295

    This system variable is deprecated (because DELAYED inserts are not supported), and you should expect it to be removed in a future release.

  • delayed_insert_timeout

    Command-Line Format --delayed-insert-timeout=#
    Deprecated Yes
    System Variable delayed_insert_timeout
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Integer
    Default Value 300
    Minimum Value 1
    Maximum Value 31536000
    Unit seconds

    This system variable is deprecated (because DELAYED inserts are not supported), and you should expect it to be removed in a future release.

  • delayed_queue_size

    Command-Line Format --delayed-queue-size=#
    Deprecated Yes
    System Variable delayed_queue_size
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Integer
    Default Value 1000
    Minimum Value 1
    Maximum Value (64-bit platforms) 18446744073709551615
    Maximum Value (32-bit platforms) 4294967295

    This system variable is deprecated (because DELAYED inserts are not supported), and you should expect it to be removed in a future release.

  • disabled_storage_engines

    Command-Line Format --disabled-storage-engines=engine[,engine]...
    System Variable disabled_storage_engines
    Scope Global
    Dynamic No
    SET_VAR Hint Applies No
    Type String
    Default Value empty string

    This variable indicates which storage engines cannot be used to create tables or tablespaces. For example, to prevent new MyISAM or FEDERATED tables from being created, start the server with these lines in the server option file:

    Press CTRL+C to copy
    [mysqld] disabled_storage_engines="MyISAM,FEDERATED"

    By default, disabled_storage_engines is empty (no engines disabled), but it can be set to a comma-separated list of one or more engines (not case-sensitive). Any engine named in the value cannot be used to create tables or tablespaces with CREATE TABLE or CREATE TABLESPACE, and cannot be used with ALTER TABLE ... ENGINE or ALTER TABLESPACE ... ENGINE to change the storage engine of existing tables or tablespaces. Attempts to do so result in an ER_DISABLED_STORAGE_ENGINE error.

    disabled_storage_engines does not restrict other DDL statements for existing tables, such as CREATE INDEX, TRUNCATE TABLE, ANALYZE TABLE, DROP TABLE, or DROP TABLESPACE. This permits a smooth transition so that existing tables or tablespaces that use a disabled engine can be migrated to a permitted engine by means such as ALTER TABLE ... ENGINE permitted_engine.

    It is permitted to set the default_storage_engine or default_tmp_storage_engine system variable to a storage engine that is disabled. This could cause applications to behave erratically or fail, although that might be a useful technique in a development environment for identifying applications that use disabled engines, so that they can be modified.

    disabled_storage_engines is disabled and has no effect if the server is started with any of these options: --initialize, --initialize-insecure, --skip-grant-tables.

  • disconnect_on_expired_password

    Command-Line Format --disconnect-on-expired-password[={OFF|ON}]
    System Variable disconnect_on_expired_password
    Scope Global
    Dynamic No
    SET_VAR Hint Applies No
    Type Boolean
    Default Value ON

    This variable controls how the server handles clients with expired passwords:

    For more information about the interaction of client and server settings relating to expired-password handling, see Section 6.2.16, 鈥淪erver Handling of Expired Passwords鈥?/a>.

  • div_precision_increment

    Command-Line Format --div-precision-increment=#
    System Variable div_precision_increment
    Scope Global, Session
    Dynamic Yes
    SET_VAR Hint Applies Yes
    Type Integer
    Default Value 4
    Minimum Value 0
    Maximum Value 30

    This variable indicates the number of digits by which to increase the scale of the result of division operations performed with the / operator. The default value is 4. The minimum and maximum values are 0 and 30, respectively. The following example illustrates the effect of increasing the default value.

    Press CTRL+C to copy
    mysql> SELECT 1/7; +--------+ | 1/7 | +--------+ | 0.1429 | +--------+ mysql> SET div_precision_increment = 12; mysql> SELECT 1/7; +----------------+ | 1/7 | +----------------+ | 0.142857142857 | +----------------+
  • dragnet.log_error_filter_rules

    Command-Line Format --dragnet.log-error-filter-rules=value
    System Variable dragnet.log_error_filter_rules
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type String
    Default Value IF prio>=INFORMATION THEN drop. IF EXISTS source_line THEN unset source_line.

    The filter rules that control operation of the log_filter_dragnet error log filter component. If log_filter_dragnet is not installed, dragnet.log_error_filter_rules is unavailable. If log_filter_dragnet is installed but not enabled, changes to dragnet.log_error_filter_rules have no effect.

    The effect of the default value is similar to the filtering performed by the log_sink_internal filter with a setting of log_error_verbosity=2.

    As of MySQL 8.0.12, the dragnet.Status status variable can be consulted to determine the result of the most recent assignment to dragnet.log_error_filter_rules.

    Prior to MySQL 8.0.12, successful assignments to dragnet.log_error_filter_rules at runtime produce a note confirming the new value:

    Press CTRL+C to copy
    mysql> SET GLOBAL dragnet.log_error_filter_rules = 'IF prio <> 0 THEN unset prio.'; Query OK, 0 rows affected, 1 warning (0.00 sec) mysql> SHOW WARNINGS\G *************************** 1. row *************************** Level: Note Code: 4569 Message: filter configuration accepted: SET @@GLOBAL.dragnet.log_error_filter_rules= 'IF prio!=ERROR THEN unset prio.';

    The value displayed by SHOW WARNINGS indicates the 鈥?span class="quote">decompiled鈥?/span> canonical representation after the rule set has been successfully parsed and compiled into internal form. Semantically, this canonical form is identical to the value assigned to dragnet.log_error_filter_rules, but there may be some differences between the assigned and canonical values, as illustrated by the preceding example:

    • The <> operator is changed to !=.

    • The numeric priority of 0 is changed to the corresponding priority symbol ERROR.

    • Optional spaces are removed.

    For additional information, see Section 5.4.2.4, 鈥淭ypes of Error Log Filtering鈥?/a>, and Section 5.5.3, 鈥淓rror Log Components鈥?/a>.

  • enterprise_encryption.maximum_rsa_key_size

    Command-Line Format --enterprise-encryption.maximum-rsa-key-size=#
    Introduced 8.0.30
    System Variable enterprise_encryption.maximum_rsa_key_size
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Integer
    Default Value 4096
    Minimum Value 2048
    Maximum Value 16384

    This variable limits the maximum size of RSA keys generated by MySQL Enterprise Encryption. The variable is available only if the MySQL Enterprise Encryption component component_enterprise_encryption is installed, which is available from MySQL 8.0.30. The variable is not available if the openssl_udf shared library is used to provide MySQL Enterprise Encryption functions.

    The lowest setting is 2048 bits, which is the minimum RSA key length that is acceptable by current best practice. The default setting is 4096 bits. The highest setting is 16384 bits. Generating longer keys can consume significant CPU resources, so you can use this setting to limit keys to a length that provides adequate security for your requirements while balancing this with resource usage. Note that the functions provided by the openssl_udf shared library allow key lengths starting at 1024 bits, and following an upgrade to the component, the minimum key length is greater than this. See Section 6.6.2, 鈥淐onfiguring MySQL Enterprise Encryption鈥?/a> for more information.

  • enterprise_encryption.rsa_support_legacy_padding

    Command-Line Format --enterprise-encryption.rsa_support_legacy_padding[={OFF|ON}]
    Introduced 8.0.30
    System Variable enterprise_encryption.rsa_support_legacy_padding
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Boolean
    Default Value OFF

    This variable controls whether encrypted data and signatures that MySQL Enterprise Encryption produced with the openssl_udf shared library functions used before MySQL 8.0.30, can be decrypted or verified by the functions of the MySQL Enterprise Encryption component component_enterprise_encryption, which is available from MySQL 8.0.30. The variable is available only if the MySQL Enterprise Encryption component is installed, and it is not available if the openssl_udf shared library is used to provide MySQL Enterprise Encryption functions.

    For the component functions to support decryption and verification for content produced by the legacy openssl_udf shared library functions, you must set the system variable padding to ON. When ON is set, if the component functions cannot decrypt or verify content when assuming it has the RSAES-OAEP or RSASSA-PSS scheme (as used by the component), they make another attempt assuming it has the RSAES-PKCS1-v1_5 or RSASSA-PKCS1-v1_5 scheme (as used by the openssl_udf shared library functions). When OFF is set, if the component functions cannot decrypt or verify content using their normal schemes, they return null output. See Section 6.6.2, 鈥淐onfiguring MySQL Enterprise Encryption鈥?/a> for more information.

  • end_markers_in_json

    Command-Line Format --end-markers-in-json[={OFF|ON}]
    System Variable end_markers_in_json
    Scope Global, Session
    Dynamic Yes
    SET_VAR Hint Applies Yes
    Type Boolean
    Default Value OFF

    Whether optimizer JSON output should add end markers. See MySQL Internals: The end_markers_in_json System Variable.

  • eq_range_index_dive_limit

    Command-Line Format --eq-range-index-dive-limit=#
    System Variable eq_range_index_dive_limit
    Scope Global, Session
    Dynamic Yes
    SET_VAR Hint Applies Yes
    Type Integer
    Default Value 200
    Minimum Value 0
    Maximum Value 4294967295

    This variable indicates the number of equality ranges in an equality comparison condition when the optimizer should switch from using index dives to index statistics in estimating the number of qualifying rows. It applies to evaluation of expressions that have either of these equivalent forms, where the optimizer uses a nonunique index to look up col_name values:

    Press CTRL+C to copy
    col_name IN(val1, ..., valN) col_name = val1 OR ... OR col_name = valN

    In both cases, the expression contains N equality ranges. The optimizer can make row estimates using index dives or index statistics. If eq_range_index_dive_limit is greater than 0, the optimizer uses existing index statistics instead of index dives if there are eq_range_index_dive_limit or more equality ranges. Thus, to permit use of index dives for up to N equality ranges, set eq_range_index_dive_limit to N + 1. To disable use of index statistics and always use index dives regardless of N, set eq_range_index_dive_limit to 0.

    For more information, see Equality Range Optimization of Many-Valued Comparisons.

    To update table index statistics for best estimates, use ANALYZE TABLE.

  • error_count

    The number of errors that resulted from the last statement that generated messages. This variable is read only. See Section 13.7.7.17, 鈥淪HOW ERRORS Statement鈥?/a>.

  • event_scheduler

    Command-Line Format --event-scheduler[=value]
    System Variable event_scheduler
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Enumeration
    Default Value ON
    Valid Values

    ON

    OFF

    DISABLED

    This variable enables or disables, and starts or stops, the Event Scheduler. The possible status values are ON, OFF, and DISABLED. Turning the Event Scheduler OFF is not the same as disabling the Event Scheduler, which requires setting the status to DISABLED. This variable and its effects on the Event Scheduler's operation are discussed in greater detail in Section 25.4.2, 鈥淓vent Scheduler Configuration鈥?/a>

  • explain_format

    Command-Line Format --explain-format=format
    Introduced 8.0.32
    System Variable explain_format
    Scope Global, Session
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Enumeration
    Default Value TRADITIONAL
    Valid Values

    JSON

    TREE

    DEFAULT

    This variable determines the default output format used by EXPLAIN in the absence of a FORMAT option when displaying a query execution plan. Possible values and their effects are listed here:

    • TRADITIONAL: Use MySQL's traditional table-based output, as if FORMAT=TRADITIONAL had been specified as part of the EXPLAIN statement. This is the variable's default value.

    • JSON: Use the JSON output format, as if FORMAT=JSON had been specified.

    • TREE: Use the tree-based output format, as if FORMAT=TREE had been specified.

    • DEFAULT: A synonym for TRADITIONAL having exactly the same effect.

      Note

      DEFAULT cannot be used as part of an EXPLAIN statement's FORMAT option.

    The setting for this variable also affects EXPLAIN ANALYZE. For this purpose, DEFAULT and TRADITIONAL are interpeted as TREE. If the value of explain_format is JSON and an EXPLAIN ANALYZE statement having no FORMAT option is issued, the statement raises an error (ER_NOT_SUPPORTED_YET).

    Using a format specifier with EXPLAIN or EXPLAIN ANALYZE overrides any setting for explain_format.

    The explain_format system variable has no effect on EXPLAIN output when this statement is used to display information about table columns.

    Setting the session value of explain_format requires no special privileges; setting it on the global level requires SYSTEM_VARIABLES_ADMIN (or the deprecated SUPER privilege). See Section 5.1.9.1, 鈥淪ystem Variable Privileges鈥?/a>.

    For more information and examples, see Obtaining Execution Plan Information.

  • explicit_defaults_for_timestamp

    Command-Line Format --explicit-defaults-for-timestamp[={OFF|ON}]
    Deprecated Yes
    System Variable explicit_defaults_for_timestamp
    Scope Global, Session
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Boolean
    Default Value ON

    This system variable determines whether the server enables certain nonstandard behaviors for default values and NULL-value handling in TIMESTAMP columns. By default, explicit_defaults_for_timestamp is enabled, which disables the nonstandard behaviors. Disabling explicit_defaults_for_timestamp results in a warning.

    As of MySQL 8.0.18, setting the session value of this system variable is no longer a restricted operation.

    If explicit_defaults_for_timestamp is disabled, the server enables the nonstandard behaviors and handles TIMESTAMP columns as follows:

    • TIMESTAMP columns not explicitly declared with the NULL attribute are automatically declared with the NOT NULL attribute. Assigning such a column a value of NULL is permitted and sets the column to the current timestamp. Exception: As of MySQL 8.0.22, attempting to insert NULL into a generated column declared as TIMESTAMP NOT NULL is rejected with an error.

    • The first TIMESTAMP column in a table, if not explicitly declared with the NULL attribute or an explicit DEFAULT or ON UPDATE attribute, is automatically declared with the DEFAULT CURRENT_TIMESTAMP and ON UPDATE CURRENT_TIMESTAMP attributes.

    • TIMESTAMP columns following the first one, if not explicitly declared with the NULL attribute or an explicit DEFAULT attribute, are automatically declared as DEFAULT '0000-00-00 00:00:00' (the 鈥?span class="quote">zero鈥?/span> timestamp). For inserted rows that specify no explicit value for such a column, the column is assigned '0000-00-00 00:00:00' and no warning occurs.

      Depending on whether strict SQL mode or the NO_ZERO_DATE SQL mode is enabled, a default value of '0000-00-00 00:00:00' may be invalid. Be aware that the TRADITIONAL SQL mode includes strict mode and NO_ZERO_DATE. See Section 5.1.11, 鈥淪erver SQL Modes鈥?/a>.

    The nonstandard behaviors just described are deprecated; expect them to be removed in a future MySQL release.

    If explicit_defaults_for_timestamp is enabled, the server disables the nonstandard behaviors and handles TIMESTAMP columns as follows:

    • It is not possible to assign a TIMESTAMP column a value of NULL to set it to the current timestamp. To assign the current timestamp, set the column to CURRENT_TIMESTAMP or a synonym such as NOW().

    • TIMESTAMP columns not explicitly declared with the NOT NULL attribute are automatically declared with the NULL attribute and permit NULL values. Assigning such a column a value of NULL sets it to NULL, not the current timestamp.

    • TIMESTAMP columns declared with the NOT NULL attribute do not permit NULL values. For inserts that specify NULL for such a column, the result is either an error for a single-row insert if strict SQL mode is enabled, or '0000-00-00 00:00:00' is inserted for multiple-row inserts with strict SQL mode disabled. In no case does assigning the column a value of NULL set it to the current timestamp.

    • TIMESTAMP columns explicitly declared with the NOT NULL attribute and without an explicit DEFAULT attribute are treated as having no default value. For inserted rows that specify no explicit value for such a column, the result depends on the SQL mode. If strict SQL mode is enabled, an error occurs. If strict SQL mode is not enabled, the column is declared with the implicit default of '0000-00-00 00:00:00' and a warning occurs. This is similar to how MySQL treats other temporal types such as DATETIME.

    • No TIMESTAMP column is automatically declared with the DEFAULT CURRENT_TIMESTAMP or ON UPDATE CURRENT_TIMESTAMP attributes. Those attributes must be explicitly specified.

    • The first TIMESTAMP column in a table is not handled differently from TIMESTAMP columns following the first one.

    If explicit_defaults_for_timestamp is disabled at server startup, this warning appears in the error log:

    Press CTRL+C to copy
    [Warning] TIMESTAMP with implicit DEFAULT value is deprecated. Please use --explicit_defaults_for_timestamp server option (see documentation for more details).

    As indicated by the warning, to disable the deprecated nonstandard behaviors, enable the explicit_defaults_for_timestamp system variable at server startup.

    Note

    explicit_defaults_for_timestamp is itself deprecated because its only purpose is to permit control over deprecated TIMESTAMP behaviors that are to be removed in a future MySQL release. When removal of those behaviors occurs, expect explicit_defaults_for_timestamp to be removed as well.

    For additional information, see Section 11.2.5, 鈥淎utomatic Initialization and Updating for TIMESTAMP and DATETIME鈥?/a>.

  • external_user

    System Variable external_user
    Scope Session
    Dynamic No
    SET_VAR Hint Applies No
    Type String

    The external user name used during the authentication process, as set by the plugin used to authenticate the client. With native (built-in) MySQL authentication, or if the plugin does not set the value, this variable is NULL. See Section 6.2.19, 鈥淧roxy Users鈥?/a>.

  • flush

    Command-Line Format --flush[={OFF|ON}]
    System Variable flush
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Boolean
    Default Value OFF

    If ON, the server flushes (synchronizes) all changes to disk after each SQL statement. Normally, MySQL does a write of all changes to disk only after each SQL statement and lets the operating system handle the synchronizing to disk. See Section B.3.3.3, 鈥淲hat to Do If MySQL Keeps Crashing鈥?/a>. This variable is set to ON if you start mysqld with the --flush option.

    Note

    If flush is enabled, the value of flush_time does not matter and changes to flush_time have no effect on flush behavior.

  • flush_time

    Command-Line Format --flush-time=#
    System Variable flush_time
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Integer
    Default Value 0
    Minimum Value 0
    Maximum Value 31536000
    Unit seconds

    If this is set to a nonzero value, all tables are closed every flush_time seconds to free up resources and synchronize unflushed data to disk. This option is best used only on systems with minimal resources.

    Note

    If flush is enabled, the value of flush_time does not matter and changes to flush_time have no effect on flush behavior.

  • foreign_key_checks

    System Variable foreign_key_checks
    Scope Global, Session
    Dynamic Yes
    SET_VAR Hint Applies Yes
    Type Boolean
    Default Value ON

    If set to 1 (the default), foreign key constraints are checked. If set to 0, foreign key constraints are ignored, with a couple of exceptions. When re-creating a table that was dropped, an error is returned if the table definition does not conform to the foreign key constraints referencing the table. Likewise, an ALTER TABLE operation returns an error if a foreign key definition is incorrectly formed. For more information, see Section 13.1.20.5, 鈥淔OREIGN KEY Constraints鈥?/a>.

    Setting this variable has the same effect on NDB tables as it does for InnoDB tables. Typically you leave this setting enabled during normal operation, to enforce referential integrity. Disabling foreign key checking can be useful for reloading InnoDB tables in an order different from that required by their parent/child relationships. See Section 13.1.20.5, 鈥淔OREIGN KEY Constraints鈥?/a>.

    Setting foreign_key_checks to 0 also affects data definition statements: DROP SCHEMA drops a schema even if it contains tables that have foreign keys that are referred to by tables outside the schema, and DROP TABLE drops tables that have foreign keys that are referred to by other tables.

    Note

    Setting foreign_key_checks to 1 does not trigger a scan of the existing table data. Therefore, rows added to the table while foreign_key_checks = 0 are not verified for consistency.

    Dropping an index required by a foreign key constraint is not permitted, even with foreign_key_checks=0. The foreign key constraint must be removed before dropping the index.

  • ft_boolean_syntax

    Command-Line Format --ft-boolean-syntax=name
    System Variable ft_boolean_syntax
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type String
    Default Value + -><()~*:""&|

    The list of operators supported by boolean full-text searches performed using IN BOOLEAN MODE. See Section 12.10.2, 鈥淏oolean Full-Text Searches鈥?/a>.

    The default variable value is '+ -><()~*:""&|'. The rules for changing the value are as follows:

    • Operator function is determined by position within the string.

    • The replacement value must be 14 characters.

    • Each character must be an ASCII nonalphanumeric character.

    • Either the first or second character must be a space.

    • No duplicates are permitted except the phrase quoting operators in positions 11 and 12. These two characters are not required to be the same, but they are the only two that may be.

    • Positions 10, 13, and 14 (which by default are set to :, &, and |) are reserved for future extensions.

  • ft_max_word_len

    Command-Line Format --ft-max-word-len=#
    System Variable ft_max_word_len
    Scope Global
    Dynamic No
    SET_VAR Hint Applies No
    Type Integer
    Default Value 84
    Minimum Value 10
    Maximum Value 84

    The maximum length of the word to be included in a MyISAM FULLTEXT index.

    Note

    FULLTEXT indexes on MyISAM tables must be rebuilt after changing this variable. Use REPAIR TABLE tbl_name QUICK.

  • ft_min_word_len

    Command-Line Format --ft-min-word-len=#
    System Variable ft_min_word_len
    Scope Global
    Dynamic No
    SET_VAR Hint Applies No
    Type Integer
    Default Value 4
    Minimum Value 1
    Maximum Value 82

    The minimum length of the word to be included in a MyISAM FULLTEXT index.

    Note

    FULLTEXT indexes on MyISAM tables must be rebuilt after changing this variable. Use REPAIR TABLE tbl_name QUICK.

  • ft_query_expansion_limit

    Command-Line Format --ft-query-expansion-limit=#
    System Variable ft_query_expansion_limit
    Scope Global
    Dynamic No
    SET_VAR Hint Applies No
    Type Integer
    Default Value 20
    Minimum Value 0
    Maximum Value 1000

    The number of top matches to use for full-text searches performed using WITH QUERY EXPANSION.

  • ft_stopword_file

    Command-Line Format --ft-stopword-file=file_name
    System Variable ft_stopword_file
    Scope Global
    Dynamic No
    SET_VAR Hint Applies No
    Type File name

    The file from which to read the list of stopwords for full-text searches on MyISAM tables. The server looks for the file in the data directory unless an absolute path name is given to specify a different directory. All the words from the file are used; comments are not honored. By default, a built-in list of stopwords is used (as defined in the storage/myisam/ft_static.c file). Setting this variable to the empty string ('') disables stopword filtering. See also Section 12.10.4, 鈥淔ull-Text Stopwords鈥?/a>.

    Note

    FULLTEXT indexes on MyISAM tables must be rebuilt after changing this variable or the contents of the stopword file. Use REPAIR TABLE tbl_name QUICK.

  • general_log

    Command-Line Format --general-log[={OFF|ON}]
    System Variable general_log
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Boolean
    Default Value OFF

    Whether the general query log is enabled. The value can be 0 (or OFF) to disable the log or 1 (or ON) to enable the log. The destination for log output is controlled by the log_output system variable; if that value is NONE, no log entries are written even if the log is enabled.

  • general_log_file

    Command-Line Format --general-log-file=file_name
    System Variable general_log_file
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type File name
    Default Value host_name.log

    The name of the general query log file. The default value is host_name.log, but the initial value can be changed with the --general_log_file option.

  • generated_random_password_length

    Command-Line Format --generated-random-password-length=#
    Introduced 8.0.18
    System Variable generated_random_password_length
    Scope Global, Session
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Integer
    Default Value 20
    Minimum Value 5
    Maximum Value 255

    The maximum number of characters permitted in random passwords generated for CREATE USER, ALTER USER, and SET PASSWORD statements. For more information, see Random Password Generation.

  • global_connection_memory_limit

    Command-Line Format --global-connection-memory-limit=#
    Introduced 8.0.28
    System Variable global_connection_memory_limit
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Integer
    Default Value 18446744073709551615
    Minimum Value 16777216
    Maximum Value 18446744073709551615
    Unit bytes

    Set the total amount of memory that can be used by all user connections; that is, Global_connection_memory should not exceed this amount. Any time that it does, any new queries from users are rejected with ER_GLOBAL_CONN_LIMIT.

    Memory used by the system users such as the MySQL root user is included in this total, but is not counted towards the disconnection limit; such users are never disconnected due to memory usage.

    Memory used by the InnoDB buffer pool is excluded from the total.

    You must have the SYSTEM_VARIABLES_ADMIN or SUPER privilege to set this variable.

  • global_connection_memory_tracking

    Command-Line Format --global-connection-memory-tracking={TRUE|FALSE}
    Introduced 8.0.28
    System Variable global_connection_memory_tracking
    Scope Global, Session
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Boolean
    Default Value FALSE

    Determines whether the server calculates Global_connection_memory. This variable must be enabled explicitly; otherwise, the memory calculation is not performed, and Global_connection_memory is not set.

    You must have the SYSTEM_VARIABLES_ADMIN or SUPER privilege to set this variable.

  • group_concat_max_len

    Command-Line Format --group-concat-max-len=#
    System Variable group_concat_max_len
    Scope Global, Session
    Dynamic Yes
    SET_VAR Hint Applies Yes
    Type Integer
    Default Value 1024
    Minimum Value 4
    Maximum Value (64-bit platforms) 18446744073709551615
    Maximum Value (32-bit platforms) 4294967295

    The maximum permitted result length in bytes for the GROUP_CONCAT() function. The default is 1024.

  • have_compress

    YES if the zlib compression library is available to the server, NO if not. If not, the COMPRESS() and UNCOMPRESS() functions cannot be used.

  • have_dynamic_loading

    YES if mysqld supports dynamic loading of plugins, NO if not. If the value is NO, you cannot use options such as --plugin-load to load plugins at server startup, or the INSTALL PLUGIN statement to load plugins at runtime.

  • have_geometry

    YES if the server supports spatial data types, NO if not.

  • have_openssl

    This variable is a synonym for have_ssl.

    As of MySQL 8.0.26, have_openssl is deprecated and subject to removal in a future MySQL version. For information about TLS properties of MySQL connection interfaces, use the tls_channel_status table.

  • have_profiling

    YES if statement profiling capability is present, NO if not. If present, the profiling system variable controls whether this capability is enabled or disabled. See Section 13.7.7.31, 鈥淪HOW PROFILES Statement鈥?/a>.

    This variable is deprecated and you should expect it to be removed in a future MySQL release.

  • have_query_cache

    The query cache was removed in MySQL 8.0.3. have_query_cache is deprecated, always has a value of NO, and you should expect it to be removed in a future MySQL release.

  • have_rtree_keys

    YES if RTREE indexes are available, NO if not. (These are used for spatial indexes in MyISAM tables.)

  • have_ssl

    Deprecated 8.0.26
    System Variable have_ssl
    Scope Global
    Dynamic No
    SET_VAR Hint Applies No
    Type String
    Valid Values

    YES (SSL support available)

    DISABLED (SSL support was compiled into server, but server was not started with necessary options to enable it)

    YES if mysqld supports SSL connections, DISABLED if the server was compiled with SSL support, but was not started with the appropriate connection-encryption options. For more information, see Section 2.9.6, 鈥淐onfiguring SSL Library Support鈥?/a>.

    As of MySQL 8.0.26, have_ssl is deprecated and subject to removal in a future MySQL version. For information about TLS properties of MySQL connection interfaces, use the tls_channel_status table.

  • have_statement_timeout

    System Variable have_statement_timeout
    Scope Global
    Dynamic No
    SET_VAR Hint Applies No
    Type Boolean

    Whether the statement execution timeout feature is available (see Statement Execution Time Optimizer Hints). The value can be NO if the background thread used by this feature could not be initialized.

  • have_symlink

    YES if symbolic link support is enabled, NO if not. This is required on Unix for support of the DATA DIRECTORY and INDEX DIRECTORY table options. If the server is started with the --skip-symbolic-links option, the value is DISABLED.

    This variable has no meaning on Windows.

    Note

    Symbolic link support, along with the --symbolic-links option that controls it, is deprecated; expect these to be removed in a future version of MySQL. In addition, the option is disabled by default. The related have_symlink system variable also is deprecated and you should expect it to be removed in a future version of MySQL.

  • histogram_generation_max_mem_size

    Command-Line Format --histogram-generation-max-mem-size=#
    System Variable histogram_generation_max_mem_size
    Scope Global, Session
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Integer
    Default Value 20000000
    Minimum Value 1000000
    Maximum Value (64-bit platforms) 18446744073709551615
    Maximum Value (32-bit platforms) 4294967295
    Unit bytes

    The maximum amount of memory available for generating histogram statistics. See Section 8.9.6, 鈥淥ptimizer Statistics鈥?/a>, and Section 13.7.3.1, 鈥淎NALYZE TABLE Statement鈥?/a>.

    Setting the session value of this system variable is a restricted operation. The session user must have privileges sufficient to set restricted session variables. See Section 5.1.9.1, 鈥淪ystem Variable Privileges鈥?/a>.

  • host_cache_size

    Command-Line Format --host-cache-size=#
    System Variable host_cache_size
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Integer
    Default Value -1 (signifies autosizing; do not assign this literal value)
    Minimum Value 0
    Maximum Value 65536

    The MySQL server maintains an in-memory host cache that contains client host name and IP address information and is used to avoid Domain Name System (DNS) lookups; see Section 5.1.12.3, 鈥淒NS Lookups and the Host Cache鈥?/a>.

    The host_cache_size variable controls the size of the host cache, as well as the size of the Performance Schema host_cache table that exposes the cache contents. Setting host_cache_size has these effects:

    • Setting the size to 0 disables the host cache. With the cache disabled, the server performs a DNS lookup every time a client connects.

    • Changing the size at runtime causes an implicit host cache flushing operation that clears the host cache, truncates the host_cache table, and unblocks any blocked hosts.

    The default value is autosized to 128, plus 1 for a value of max_connections up to 500, plus 1 for every increment of 20 over 500 in the max_connections value, capped to a limit of 2000.

    Using the --skip-host-cache option is similar to setting the host_cache_size system variable to 0, but host_cache_size is more flexible because it can also be used to resize, enable, and disable the host cache at runtime, not just at server startup.

    Starting the server with --skip-host-cache does not prevent runtime changes to the value of host_cache_size, but such changes have no effect and the cache is not re-enabled even if host_cache_size is set larger than 0.

    Setting the host_cache_size system variable rather than the --skip-host-cache option is preferred for the reasons given in the previous paragraph. In addition, the --skip-host-cache option is deprecated and its removal is expected in a future version of MySQL; in MySQL 8.0.29 and later, using the option raises a warning.

  • hostname

    System Variable hostname
    Scope Global
    Dynamic No
    SET_VAR Hint Applies No
    Type String

    The server sets this variable to the server host name at startup. The maximum length is 255 characters as of MySQL 8.0.17, per RFC 1034, and 60 characters before that.

  • identity

    This variable is a synonym for the last_insert_id variable. It exists for compatibility with other database systems. You can read its value with SELECT @@identity, and set it using SET identity.

  • init_connect

    Command-Line Format --init-connect=name
    System Variable init_connect
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type String

    A string to be executed by the server for each client that connects. The string consists of one or more SQL statements, separated by semicolon characters.

    For users that have the CONNECTION_ADMIN privilege (or the deprecated SUPER privilege), the content of init_connect is not executed. This is done so that an erroneous value for init_connect does not prevent all clients from connecting. For example, the value might contain a statement that has a syntax error, thus causing client connections to fail. Not executing init_connect for users that have the CONNECTION_ADMIN or SUPER privilege enables them to open a connection and fix the init_connect value.

    init_connect execution is skipped for any client user with an expired password. This is done because such a user cannot execute arbitrary statements, and thus init_connect execution fails, leaving the client unable to connect. Skipping init_connect execution enables the user to connect and change password.

    The server discards any result sets produced by statements in the value of init_connect.

  • information_schema_stats_expiry

    Command-Line Format --information-schema-stats-expiry=#
    System Variable information_schema_stats_expiry
    Scope Global, Session
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Integer
    Default Value 86400
    Minimum Value 0
    Maximum Value 31536000
    Unit seconds

    Some INFORMATION_SCHEMA tables contain columns that provide table statistics:

    Press CTRL+C to copy
    STATISTICS.CARDINALITY TABLES.AUTO_INCREMENT TABLES.AVG_ROW_LENGTH TABLES.CHECKSUM TABLES.CHECK_TIME TABLES.CREATE_TIME TABLES.DATA_FREE TABLES.DATA_LENGTH TABLES.INDEX_LENGTH TABLES.MAX_DATA_LENGTH TABLES.TABLE_ROWS TABLES.UPDATE_TIME

    Those columns represent dynamic table metadata; that is, information that changes as table contents change.

    By default, MySQL retrieves cached values for those columns from the mysql.index_stats and mysql.table_stats dictionary tables when the columns are queried, which is more efficient than retrieving statistics directly from the storage engine. If cached statistics are not available or have expired, MySQL retrieves the latest statistics from the storage engine and caches them in the mysql.index_stats and mysql.table_stats dictionary tables. Subsequent queries retrieve the cached statistics until the cached statistics expire. A server restart or the first opening of the mysql.index_stats and mysql.table_stats tables do not update cached statistics automatically.

    The information_schema_stats_expiry session variable defines the period of time before cached statistics expire. The default is 86400 seconds (24 hours), but the time period can be extended to as much as one year.

    To update cached values at any time for a given table, use ANALYZE TABLE.

    To always retrieve the latest statistics directly from the storage engine and bypass cached values, set information_schema_stats_expiry to 0.

    Querying statistics columns does not store or update statistics in the mysql.index_stats and mysql.table_stats dictionary tables under these circumstances:

    The statistics cache may be updated during a multiple-statement transaction before it is known whether the transaction commits. As a result, the cache may contain information that does not correspond to a known committed state. This can occur with autocommit=0 or after START TRANSACTION.

    information_schema_stats_expiry is a session variable, and each client session can define its own expiration value. Statistics that are retrieved from the storage engine and cached by one session are available to other sessions.

    For related information, see Section 8.2.3, 鈥淥ptimizing INFORMATION_SCHEMA Queries鈥?/a>.

  • init_file

    Command-Line Format --init-file=file_name
    System Variable init_file
    Scope Global
    Dynamic No
    SET_VAR Hint Applies No
    Type File name

    If specified, this variable names a file containing SQL statements to be read and executed during the startup process. Prior to MySQL 8.0.18, each statement must be on a single line and should not include comments. As of MySQL 8.0.18, the acceptable format for statements in the file is expanded to support these constructs:

    • delimiter ;, to set the statement delimiter to the ; character.

    • delimiter $$, to set the statement delimiter to the $$ character sequence.

    • Multiple statements on the same line, delimited by the current delimiter.

    • Multiple-line statements.

    • Comments from a # character to the end of the line.

    • Comments from a --  sequence to the end of the line.

    • C-style comments from a /* sequence to the following */ sequence, including over multiple lines.

    • Multiple-line string literals enclosed within either single quote (') or double quote (") characters.

    If the server is started with the --initialize or --initialize-insecure option, it operates in bootstrap mode and some functionality is unavailable that limits the statements permitted in the file. These include statements that relate to account management (such as CREATE USER or GRANT), replication, and global transaction identifiers. See Section 17.1.3, 鈥淩eplication with Global Transaction Identifiers鈥?/a>.

    As of MySQL 8.0.17, threads created during server startup are used for tasks such as creating the data dictionary, running upgrade procedures, and creating system tables. To ensure a stable and predictable environment, these threads are executed with the server built-in defaults for some system variables, such as sql_mode, character_set_server, collation_server, completion_type, explicit_defaults_for_timestamp, and default_table_encryption.

    These threads are also used to execute the statements in any file specified with init_file when starting the server, so such statements execute with the server's built-in default values for those system variables.

  • innodb_xxx

    InnoDB system variables are listed in Section 15.14, 鈥淚nnoDB Startup Options and System Variables鈥?/a>. These variables control many aspects of storage, memory use, and I/O patterns for InnoDB tables, and are especially important now that InnoDB is the default storage engine.

  • insert_id

    The value to be used by the following INSERT or ALTER TABLE statement when inserting an AUTO_INCREMENT value. This is mainly used with the binary log.

  • interactive_timeout

    Command-Line Format --interactive-timeout=#
    System Variable interactive_timeout
    Scope Global, Session
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Integer
    Default Value 28800
    Minimum Value 1
    Maximum Value 31536000
    Unit seconds

    The number of seconds the server waits for activity on an interactive connection before closing it. An interactive client is defined as a client that uses the CLIENT_INTERACTIVE option to mysql_real_connect(). See also wait_timeout.

  • internal_tmp_disk_storage_engine

    Command-Line Format --internal-tmp-disk-storage-engine=#
    Removed 8.0.16
    System Variable internal_tmp_disk_storage_engine
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Enumeration
    Default Value INNODB
    Valid Values

    MYISAM

    INNODB

    Important

    In MySQL 8.0.16 and later, on-disk internal temporary tables always use the InnoDB storage engine; as of MySQL 8.0.16, this variable has been removed and is thus no longer supported.

    Prior to MySQL 8.0.16, this variable determines the storage engine used for on-disk internal temporary tables (see Storage Engine for On-Disk Internal Temporary Tables). Permitted values are MYISAM and INNODB (the default).

  • internal_tmp_mem_storage_engine

    Command-Line Format --internal-tmp-mem-storage-engine=#
    System Variable internal_tmp_mem_storage_engine
    Scope Global, Session
    Dynamic Yes
    SET_VAR Hint Applies Yes
    Type Enumeration
    Default Value TempTable
    Valid Values

    MEMORY

    TempTable

    The storage engine for in-memory internal temporary tables (see Section 8.4.4, 鈥淚nternal Temporary Table Use in MySQL鈥?/a>). Permitted values are TempTable (the default) and MEMORY.

    The optimizer uses the storage engine defined by internal_tmp_mem_storage_engine for in-memory internal temporary tables.

    From MySQL 8.0.27, configuring a session setting for internal_tmp_mem_storage_engine requires the SESSION_VARIABLES_ADMIN or SYSTEM_VARIABLES_ADMIN privilege.

  • join_buffer_size

    Command-Line Format --join-buffer-size=#
    System Variable join_buffer_size
    Scope Global, Session
    Dynamic Yes
    SET_VAR Hint Applies Yes
    Type Integer
    Default Value 262144
    Minimum Value 128
    Maximum Value (Windows) 4294967168
    Maximum Value (Other, 64-bit platforms) 18446744073709551488
    Maximum Value (Other, 32-bit platforms) 4294967168
    Unit bytes
    Block Size 128

    The minimum size of the buffer that is used for plain index scans, range index scans, and joins that do not use indexes and thus perform full table scans. In MySQL 8.0.18 and later, this variable also controls the amount of memory used for hash joins. Normally, the best way to get fast joins is to add indexes. Increase the value of join_buffer_size to get a faster full join when adding indexes is not possible. One join buffer is allocated for each full join between two tables. For a complex join between several tables for which indexes are not used, multiple join buffers might be necessary.

    The default is 256KB. The maximum permissible setting for join_buffer_size is 4GB鈭?. Larger values are permitted for 64-bit platforms (except 64-bit Windows, for which large values are truncated to 4GB鈭? with a warning). The block size is 128, and a value that is not an exact multiple of the block size is rounded down to the next lower multiple of the block size by MySQL Server before storing the value for the system variable. The parser allows values up to the maximum unsigned integer value for the platform (4294967295 or 232鈭? for a 32-bit system, 18446744073709551615 or 264鈭? for a 64-bit system) but the actual maximum is a block size lower.

    Unless a Block Nested-Loop or Batched Key Access algorithm is used, there is no gain from setting the buffer larger than required to hold each matching row, and all joins allocate at least the minimum size, so use caution in setting this variable to a large value globally. It is better to keep the global setting small and change the session setting to a larger value only in sessions that are doing large joins, or change the setting on a per-query basis by using a SET_VAR optimizer hint (see Section 8.9.3, 鈥淥ptimizer Hints鈥?/a>). Memory allocation time can cause substantial performance drops if the global size is larger than needed by most queries that use it.

    When Block Nested-Loop is used, a larger join buffer can be beneficial up to the point where all required columns from all rows in the first table are stored in the join buffer. This depends on the query; the optimal size may be smaller than holding all rows from the first tables.

    When Batched Key Access is used, the value of join_buffer_size defines how large the batch of keys is in each request to the storage engine. The larger the buffer, the more sequential access is made to the right hand table of a join operation, which can significantly improve performance.

    For additional information about join buffering, see Section 8.2.1.7, 鈥淣ested-Loop Join Algorithms鈥?/a>. For information about Batched Key Access, see Section 8.2.1.12, 鈥淏lock Nested-Loop and Batched Key Access Joins鈥?/a>. For information about hash joins, see Section 8.2.1.4, 鈥淗ash Join Optimization鈥?/a>.

  • keep_files_on_create

    Command-Line Format --keep-files-on-create[={OFF|ON}]
    System Variable keep_files_on_create
    Scope Global, Session
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Boolean
    Default Value OFF

    If a MyISAM table is created with no DATA DIRECTORY option, the .MYD file is created in the database directory. By default, if MyISAM finds an existing .MYD file in this case, it overwrites it. The same applies to .MYI files for tables created with no INDEX DIRECTORY option. To suppress this behavior, set the keep_files_on_create variable to ON (1), in which case MyISAM does not overwrite existing files and returns an error instead. The default value is OFF (0).

    If a MyISAM table is created with a DATA DIRECTORY or INDEX DIRECTORY option and an existing .MYD or .MYI file is found, MyISAM always returns an error. It does not overwrite a file in the specified directory.

  • key_buffer_size

    Command-Line Format --key-buffer-size=#
    System Variable key_buffer_size
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Integer
    Default Value 8388608
    Minimum Value 0
    Maximum Value (64-bit platforms) OS_PER_PROCESS_LIMIT
    Maximum Value (32-bit platforms) 4294967295
    Unit bytes

    Index blocks for MyISAM tables are buffered and are shared by all threads. key_buffer_size is the size of the buffer used for index blocks. The key buffer is also known as the key cache.

    The minimum permissible setting is 0, but you cannot set key_buffer_size to 0 dynamically. A setting of 0 drops the key cache, which is not permitted at runtime. Setting key_buffer_size to 0 is permitted only at startup, in which case the key cache is not initialized. Changing the key_buffer_size setting at runtime from a value of 0 to a permitted non-zero value initializes the key cache.

    key_buffer_size can be increased or decreased only in increments or multiples of 4096 bytes. Increasing or decreasing the setting by a nonconforming value produces a warning and truncates the setting to a conforming value.

    The maximum permissible setting for key_buffer_size is 4GB鈭? on 32-bit platforms. Larger values are permitted for 64-bit platforms. The effective maximum size might be less, depending on your available physical RAM and per-process RAM limits imposed by your operating system or hardware platform. The value of this variable indicates the amount of memory requested. Internally, the server allocates as much memory as possible up to this amount, but the actual allocation might be less.

    You can increase the value to get better index handling for all reads and multiple writes; on a system whose primary function is to run MySQL using the MyISAM storage engine, 25% of the machine's total memory is an acceptable value for this variable. However, you should be aware that, if you make the value too large (for example, more than 50% of the machine's total memory), your system might start to page and become extremely slow. This is because MySQL relies on the operating system to perform file system caching for data reads, so you must leave some room for the file system cache. You should also consider the memory requirements of any other storage engines that you may be using in addition to MyISAM.

    For even more speed when writing many rows at the same time, use LOCK TABLES. See Section 8.2.5.1, 鈥淥ptimizing INSERT Statements鈥?/a>.

    You can check the performance of the key buffer by issuing a SHOW STATUS statement and examining the Key_read_requests, Key_reads, Key_write_requests, and Key_writes status variables. (See Section 13.7.7, 鈥淪HOW Statements鈥?/a>.) The Key_reads/Key_read_requests ratio should normally be less than 0.01. The Key_writes/Key_write_requests ratio is usually near 1 if you are using mostly updates and deletes, but might be much smaller if you tend to do updates that affect many rows at the same time or if you are using the DELAY_KEY_WRITE table option.

    The fraction of the key buffer in use can be determined using key_buffer_size in conjunction with the Key_blocks_unused status variable and the buffer block size, which is available from the key_cache_block_size system variable:

    Press CTRL+C to copy
    1 - ((Key_blocks_unused * key_cache_block_size) / key_buffer_size)

    This value is an approximation because some space in the key buffer is allocated internally for administrative structures. Factors that influence the amount of overhead for these structures include block size and pointer size. As block size increases, the percentage of the key buffer lost to overhead tends to decrease. Larger blocks results in a smaller number of read operations (because more keys are obtained per read), but conversely an increase in reads of keys that are not examined (if not all keys in a block are relevant to a query).

    It is possible to create multiple MyISAM key caches. The size limit of 4GB applies to each cache individually, not as a group. See Section 8.10.2, 鈥淭he MyISAM Key Cache鈥?/a>.

  • key_cache_age_threshold

    Command-Line Format --key-cache-age-threshold=#
    System Variable key_cache_age_threshold
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Integer
    Default Value 300
    Minimum Value 100
    Maximum Value (64-bit platforms) 18446744073709551516
    Maximum Value (32-bit platforms) 4294967196
    Block Size 100

    This value controls the demotion of buffers from the hot sublist of a key cache to the warm sublist. Lower values cause demotion to happen more quickly. The minimum value is 100. The default value is 300. See Section 8.10.2, 鈥淭he MyISAM Key Cache鈥?/a>.

    The block size is 100. A value that is not an exact multiple of the block size is rounded down to the next lower multiple of the block size by MySQL Server before storing the value for the system variable. The parser allows values up to the maximum unsigned integer value for the platform (4294967295 or 232鈭? for a 32-bit system, 18446744073709551615 or 264鈭? for a 64-bit system) but the actual maximum is a block size lower.

  • key_cache_block_size

    Command-Line Format --key-cache-block-size=#
    System Variable key_cache_block_size
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Integer
    Default Value 1024
    Minimum Value 512
    Maximum Value 16384
    Unit bytes
    Block Size 512

    The size in bytes of blocks in the key cache. The default value is 1024. See Section 8.10.2, 鈥淭he MyISAM Key Cache鈥?/a>.

  • key_cache_division_limit

    Command-Line Format --key-cache-division-limit=#
    System Variable key_cache_division_limit
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Integer
    Default Value 100
    Minimum Value 1
    Maximum Value 100

    The division point between the hot and warm sublists of the key cache buffer list. The value is the percentage of the buffer list to use for the warm sublist. Permissible values range from 1 to 100. The default value is 100. See Section 8.10.2, 鈥淭he MyISAM Key Cache鈥?/a>.

  • large_files_support

    System Variable large_files_support
    Scope Global
    Dynamic No
    SET_VAR Hint Applies No
    Type Boolean

    Whether mysqld was compiled with options for large file support.

  • large_pages

    Command-Line Format --large-pages[={OFF|ON}]
    System Variable large_pages
    Scope Global
    Dynamic No
    SET_VAR Hint Applies No
    Platform Specific Linux
    Type Boolean
    Default Value OFF

    Whether large page support is enabled (via the --large-pages option). See Section 8.12.3.2, 鈥淓nabling Large Page Support鈥?/a>.

  • large_page_size

    System Variable large_page_size
    Scope Global
    Dynamic No
    SET_VAR Hint Applies No
    Type Integer
    Default Value 0
    Minimum Value 0
    Maximum Value 65535
    Unit bytes

    If large page support is enabled, this shows the size of memory pages. Large memory pages are supported only on Linux; on other platforms, the value of this variable is always 0. See Section 8.12.3.2, 鈥淓nabling Large Page Support鈥?/a>.

  • last_insert_id

    The value to be returned from LAST_INSERT_ID(). This is stored in the binary log when you use LAST_INSERT_ID() in a statement that updates a table. Setting this variable does not update the value returned by the mysql_insert_id() C API function.

  • lc_messages

    Command-Line Format --lc-messages=name
    System Variable lc_messages
    Scope Global, Session
    Dynamic Yes
    SET_VAR Hint Applies No
    Type String
    Default Value en_US

    The locale to use for error messages. The default is en_US. The server converts the argument to a language name and combines it with the value of lc_messages_dir to produce the location for the error message file. See Section 10.12, 鈥淪etting the Error Message Language鈥?/a>.

  • lc_messages_dir

    Command-Line Format --lc-messages-dir=dir_name
    System Variable lc_messages_dir
    Scope Global
    Dynamic No
    SET_VAR Hint Applies No
    Type Directory name

    The directory where error messages are located. The server uses the value together with the value of lc_messages to produce the location for the error message file. See Section 10.12, 鈥淪etting the Error Message Language鈥?/a>.

  • lc_time_names

    Command-Line Format --lc-time-names=value
    System Variable lc_time_names
    Scope Global, Session
    Dynamic Yes
    SET_VAR Hint Applies No
    Type String

    This variable specifies the locale that controls the language used to display day and month names and abbreviations. This variable affects the output from the DATE_FORMAT(), DAYNAME() and MONTHNAME() functions. Locale names are POSIX-style values such as 'ja_JP' or 'pt_BR'. The default value is 'en_US' regardless of your system's locale setting. For further information, see Section 10.16, 鈥淢ySQL Server Locale Support鈥?/a>.

  • license

    System Variable license
    Scope Global
    Dynamic No
    SET_VAR Hint Applies No
    Type String
    Default Value GPL

    The type of license the server has.

  • local_infile

    Command-Line Format --local-infile[={OFF|ON}]
    System Variable local_infile
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Boolean
    Default Value OFF

    This variable controls server-side LOCAL capability for LOAD DATA statements. Depending on the local_infile setting, the server refuses or permits local data loading by clients that have LOCAL enabled on the client side.

    To explicitly cause the server to refuse or permit LOAD DATA LOCAL statements (regardless of how client programs and libraries are configured at build time or runtime), start mysqld with local_infile disabled or enabled, respectively. local_infile can also be set at runtime. For more information, see Section 6.1.6, 鈥淪ecurity Considerations for LOAD DATA LOCAL鈥?/a>.

  • lock_wait_timeout

    Command-Line Format --lock-wait-timeout=#
    System Variable lock_wait_timeout
    Scope Global, Session
    Dynamic Yes
    SET_VAR Hint Applies Yes
    Type Integer
    Default Value 31536000
    Minimum Value 1
    Maximum Value 31536000
    Unit seconds

    This variable specifies the timeout in seconds for attempts to acquire metadata locks. The permissible values range from 1 to 31536000 (1 year). The default is 31536000.

    This timeout applies to all statements that use metadata locks. These include DML and DDL operations on tables, views, stored procedures, and stored functions, as well as LOCK TABLES, FLUSH TABLES WITH READ LOCK, and HANDLER statements.

    This timeout does not apply to implicit accesses to system tables in the mysql database, such as grant tables modified by GRANT or REVOKE statements or table logging statements. The timeout does apply to system tables accessed directly, such as with SELECT or UPDATE.

    The timeout value applies separately for each metadata lock attempt. A given statement can require more than one lock, so it is possible for the statement to block for longer than the lock_wait_timeout value before reporting a timeout error. When lock timeout occurs, ER_LOCK_WAIT_TIMEOUT is reported.

    lock_wait_timeout also defines the amount of time that a LOCK INSTANCE FOR BACKUP statement waits for a lock before giving up.

  • locked_in_memory

    System Variable locked_in_memory
    Scope Global
    Dynamic No
    SET_VAR Hint Applies No
    Type Boolean
    Default Value OFF

    Whether mysqld was locked in memory with --memlock.

  • log_error

    Command-Line Format --log-error[=file_name]
    System Variable log_error
    Scope Global
    Dynamic No
    SET_VAR Hint Applies No
    Type File name

    The default error log destination. If the destination is the console, the value is stderr. Otherwise, the destination is a file and the log_error value is the file name. See Section 5.4.2, 鈥淭he Error Log鈥?/a>.

  • log_error_services

    Command-Line Format --log-error-services=value
    System Variable log_error_services
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type String
    Default Value log_filter_internal; log_sink_internal

    The components to enable for error logging. The variable may contain a list with 0, 1, or many elements. In the latter case, elements may be delimited by semicolon or (as of MySQL 8.0.12) comma, optionally followed by space. A given setting cannot use both semicolon and comma separators. Component order is significant because the server executes components in the order listed.

    From MySQL 8.0.30, any loadable (not built in) component named in the log_error_services is implicitly loaded if it is not already loaded. Before MySQL 8.0.30, any loadable (not built in) component named in the log_error_services value must first be installed with INSTALL COMPONENT. For more information, see Section 5.4.2.1, 鈥淓rror Log Configuration鈥?/a>.

  • log_error_suppression_list

    Command-Line Format --log-error-suppression-list=value
    Introduced 8.0.13
    System Variable log_error_suppression_list
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type String
    Default Value empty string

    The log_error_suppression_list system variable applies to events intended for the error log and specifies which events to suppress when they occur with a priority of WARNING or INFORMATION. For example, if a particular type of warning is considered undesirable 鈥?span class="quote">noise鈥?/span> in the error log because it occurs frequently but is not of interest, it can be suppressed. This variable affects filtering performed by the log_filter_internal error log filter component, which is enabled by default (see Section 5.5.3, 鈥淓rror Log Components鈥?/a>). If log_filter_internal is disabled, log_error_suppression_list has no effect.

    The log_error_suppression_list value may be the empty string for no suppression, or a list of one or more comma-separated values indicating the error codes to suppress. Error codes may be specified in symbolic or numeric form. A numeric code may be specified with or without the MY- prefix. Leading zeros in the numeric part are not significant. Examples of permitted code formats:

    Press CTRL+C to copy
    ER_SERVER_SHUTDOWN_COMPLETE MY-000031 000031 MY-31 31

    Symbolic values are preferable to numeric values for readability and portability. For information about the permitted error symbols and numbers, see MySQL 8.0 Error Message Reference.

    The effect of log_error_suppression_list combines with that of log_error_verbosity. For additional information, see Section 5.4.2.5, 鈥淧riority-Based Error Log Filtering (log_filter_internal)鈥?/a>.

  • log_error_verbosity

    Command-Line Format --log-error-verbosity=#
    System Variable log_error_verbosity
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Integer
    Default Value 2
    Minimum Value 1
    Maximum Value 3

    The log_error_verbosity system variable specifies the verbosity for handling events intended for the error log. This variable affects filtering performed by the log_filter_internal error log filter component, which is enabled by default (see Section 5.5.3, 鈥淓rror Log Components鈥?/a>). If log_filter_internal is disabled, log_error_verbosity has no effect.

    Events intended for the error log have a priority of ERROR, WARNING, or INFORMATION. log_error_verbosity controls verbosity based on which priorities to permit for messages written to the log, as shown in the following table.

    log_error_verbosity Value Permitted Message Priorities
    1 ERROR
    2 ERROR, WARNING
    3 ERROR, WARNING, INFORMATION

    There is also a priority of SYSTEM. System messages about non-error situations are printed to the error log regardless of the log_error_verbosity value. These messages include startup and shutdown messages, and some significant changes to settings.

    The effect of log_error_verbosity combines with that of log_error_suppression_list. For additional information, see Section 5.4.2.5, 鈥淧riority-Based Error Log Filtering (log_filter_internal)鈥?/a>.

  • log_output

    Command-Line Format --log-output=name
    System Variable log_output
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Set
    Default Value FILE
    Valid Values

    TABLE

    FILE

    NONE

    The destination or destinations for general query log and slow query log output. The value is a list one or more comma-separated words chosen from TABLE, FILE, and NONE. TABLE selects logging to the general_log and slow_log tables in the mysql system schema. FILE selects logging to log files. NONE disables logging. If NONE is present in the value, it takes precedence over any other words that are present. TABLE and FILE can both be given to select both log output destinations.

    This variable selects log output destinations, but does not enable log output. To do that, enable the general_log and slow_query_log system variables. For FILE logging, the general_log_file and slow_query_log_file system variables determine the log file locations. For more information, see Section 5.4.1, 鈥淪electing General Query Log and Slow Query Log Output Destinations鈥?/a>.

  • log_queries_not_using_indexes

    Command-Line Format --log-queries-not-using-indexes[={OFF|ON}]
    System Variable log_queries_not_using_indexes
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Boolean
    Default Value OFF

    If you enable this variable with the slow query log enabled, queries that are expected to retrieve all rows are logged. See Section 5.4.5, 鈥淭he Slow Query Log鈥?/a>. This option does not necessarily mean that no index is used. For example, a query that uses a full index scan uses an index but would be logged because the index would not limit the number of rows.

  • log_raw

    Command-Line Format --log-raw[={OFF|ON}]
    System Variable (鈮?8.0.19) log_raw
    Scope (鈮?8.0.19) Global
    Dynamic (鈮?8.0.19) Yes
    SET_VAR Hint Applies (鈮?8.0.19) No
    Type Boolean
    Default Value OFF

    The log_raw system variable is initially set to the value of the --log-raw option. See the description of that option for more information. The system variable may also be set at runtime to change password masking behavior.

  • log_slow_admin_statements

    Command-Line Format --log-slow-admin-statements[={OFF|ON}]
    System Variable log_slow_admin_statements
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Boolean
    Default Value OFF

    Include slow administrative statements in the statements written to the slow query log. Administrative statements include ALTER TABLE, ANALYZE TABLE, CHECK TABLE, CREATE INDEX, DROP INDEX, OPTIMIZE TABLE, and REPAIR TABLE.

  • log_slow_extra

    Command-Line Format --log-slow-extra[={OFF|ON}]
    Introduced 8.0.14
    System Variable log_slow_extra
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Boolean
    Default Value OFF

    If the slow query log is enabled and the output destination includes FILE, the server writes additional fields to log file lines that provide information about slow statements. See Section 5.4.5, 鈥淭he Slow Query Log鈥?/a>. TABLE output is unaffected.

  • log_syslog

    Command-Line Format --log-syslog[={OFF|ON}]
    Deprecated Yes (removed in 8.0.13)
    System Variable log_syslog
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Boolean
    Default Value ON (when error logging to system log is enabled)

    Prior to MySQL 8.0, this variable controlled whether to perform error logging to the system log (the Event Log on Windows, and syslog on Unix and Unix-like systems).

    In MySQL 8.0, the log_sink_syseventlog log component implements error logging to the system log (see Section 5.4.2.8, 鈥淓rror Logging to the System Log鈥?/a>), so this type of logging can be enabled by adding that component to the log_error_services system variable. log_syslog is removed. (Prior to MySQL 8.0.13, log_syslog exists but is deprecated and has no effect.)

  • log_syslog_facility

    Command-Line Format --log-syslog-facility=value
    Removed 8.0.13
    System Variable log_syslog_facility
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type String
    Default Value daemon

    This variable was removed in MySQL 8.0.13 and replaced by syseventlog.facility.

  • log_syslog_include_pid

    Command-Line Format --log-syslog-include-pid[={OFF|ON}]
    Removed 8.0.13
    System Variable log_syslog_include_pid
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Boolean
    Default Value ON

    This variable was removed in MySQL 8.0.13 and replaced by syseventlog.include_pid.

  • log_syslog_tag

    Command-Line Format --log-syslog-tag=tag
    Removed 8.0.13
    System Variable log_syslog_tag
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type String
    Default Value empty string

    This variable was removed in MySQL 8.0.13 and replaced by syseventlog.tag.

  • log_timestamps

    Command-Line Format --log-timestamps=#
    System Variable log_timestamps
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Enumeration
    Default Value UTC
    Valid Values

    UTC

    SYSTEM

    This variable controls the time zone of timestamps in messages written to the error log, and in general query log and slow query log messages written to files. It does not affect the time zone of general query log and slow query log messages written to tables (mysql.general_log, mysql.slow_log). Rows retrieved from those tables can be converted from the local system time zone to any desired time zone with CONVERT_TZ() or by setting the session time_zone system variable.

    Permitted log_timestamps values are UTC (the default) and SYSTEM (the local system time zone).

    Timestamps are written using ISO 8601 / RFC 3339 format: YYYY-MM-DDThh:mm:ss.uuuuuu plus a tail value of Z signifying Zulu time (UTC) or 卤hh:mm (an offset from UTC).

  • log_throttle_queries_not_using_indexes

    Command-Line Format --log-throttle-queries-not-using-indexes=#
    System Variable log_throttle_queries_not_using_indexes
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Integer
    Default Value 0
    Minimum Value 0
    Maximum Value 4294967295

    If log_queries_not_using_indexes is enabled, the log_throttle_queries_not_using_indexes variable limits the number of such queries per minute that can be written to the slow query log. A value of 0 (the default) means 鈥?span class="quote">no limit鈥?/span>. For more information, see Section 5.4.5, 鈥淭he Slow Query Log鈥?/a>.

  • long_query_time

    Command-Line Format --long-query-time=#
    System Variable long_query_time
    Scope Global, Session
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Numeric
    Default Value 10
    Minimum Value 0
    Maximum Value 31536000
    Unit seconds

    If a query takes longer than this many seconds, the server increments the Slow_queries status variable. If the slow query log is enabled, the query is logged to the slow query log file. This value is measured in real time, not CPU time, so a query that is under the threshold on a lightly loaded system might be above the threshold on a heavily loaded one. The minimum and default values of long_query_time are 0 and 10, respectively. The maximum is 31536000, which is 365 days in seconds. The value can be specified to a resolution of microseconds. See Section 5.4.5, 鈥淭he Slow Query Log鈥?/a>.

    Smaller values of this variable result in more statements being considered long-running, with the result that more space is required for the slow query log. For very small values (less than one second), the log may grow quite large in a small time. Increasing the number of statements considered long-running may also result in false positives for the 鈥?span class="quote">excessive Number of Long Running Processes鈥?/span> alert in MySQL Enterprise Monitor, especially if Group Replication is enabled. For these reasons, very small values should be used in test environments only, or, in production environments, only for a short period.

    mysqldump performs a full table scan, which means its queries can often exceed a long_query_time setting that is useful for regular queries. From MySQL 8.0.30, if you want to exclude most or all of mysqldump鈥檚 queries from the slow query log, you can set mysqldump鈥檚 --mysqld-long-query-time command line option to change the session value of the system variable to a higher value.

  • low_priority_updates

    Command-Line Format --low-priority-updates[={OFF|ON}]
    System Variable low_priority_updates
    Scope Global, Session
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Boolean
    Default Value OFF

    If set to 1, all INSERT, UPDATE, DELETE, and LOCK TABLE WRITE statements wait until there is no pending SELECT or LOCK TABLE READ on the affected table. The same effect can be obtained using {INSERT | REPLACE | DELETE | UPDATE} LOW_PRIORITY ... to lower the priority of only one query. This variable affects only storage engines that use only table-level locking (such as MyISAM, MEMORY, and MERGE). See Section 8.11.2, 鈥淭able Locking Issues鈥?/a>.

    As of MySQL 8.0.27, setting the session value of this system variable is a restricted operation. The session user must have privileges sufficient to set restricted session variables. See Section 5.1.9.1, 鈥淪ystem Variable Privileges鈥?/a>.

  • lower_case_file_system

    System Variable lower_case_file_system
    Scope Global
    Dynamic No
    SET_VAR Hint Applies No
    Type Boolean

    This variable describes the case sensitivity of file names on the file system where the data directory is located. OFF means file names are case-sensitive, ON means they are not case-sensitive. This variable is read only because it reflects a file system attribute and setting it would have no effect on the file system.

  • lower_case_table_names

    Command-Line Format --lower-case-table-names[=#]
    System Variable lower_case_table_names
    Scope Global
    Dynamic No
    SET_VAR Hint Applies No
    Type Integer
    Default Value (macOS) 2
    Default Value (Unix) 0
    Default Value (Windows) 1
    Minimum Value 0
    Maximum Value 2

    If set to 0, table names are stored as specified and comparisons are case-sensitive. If set to 1, table names are stored in lowercase on disk and comparisons are not case-sensitive. If set to 2, table names are stored as given but compared in lowercase. This option also applies to database names and table aliases. For additional details, see Section 9.2.3, 鈥淚dentifier Case Sensitivity鈥?/a>.

    The default value of this variable is platform-dependent (see lower_case_file_system). On Linux and other Unix-like systems, the default is 0. On Windows the default value is 1. On macOS, the default value is 2. On Linux (and other Unix-like systems), setting the value to 2 is not supported; the server forces the value to 0 instead.

    You should not set lower_case_table_names to 0 if you are running MySQL on a system where the data directory resides on a case-insensitive file system (such as on Windows or macOS). It is an unsupported combination that could result in a hang condition when running an INSERT INTO ... SELECT ... FROM tbl_name operation with the wrong tbl_name lettercase. With MyISAM, accessing table names using different lettercases could cause index corruption.

    An error message is printed and the server exits if you attempt to start the server with --lower_case_table_names=0 on a case-insensitive file system.

    The setting of this variable affects the behavior of replication filtering options with regard to case sensitivity. For more information, see Section 17.2.5, 鈥淗ow Servers Evaluate Replication Filtering Rules鈥?/a>.

    It is prohibited to start the server with a lower_case_table_names setting that is different from the setting used when the server was initialized. The restriction is necessary because collations used by various data dictionary table fields are determined by the setting defined when the server is initialized, and restarting the server with a different setting would introduce inconsistencies with respect to how identifiers are ordered and compared.

    It is therefore necessary to configure lower_case_table_names to the desired setting before initializing the server. In most cases, this requires configuring lower_case_table_names in a MySQL option file before starting the MySQL server for the first time. For APT installations on Debian and Ubuntu, however, the server is initialized for you, and there is no opportunity to configure the setting in an option file beforehand. You must therefore use the debconf-set-selection utility prior to installing MySQL using APT to enable lower_case_table_names. To do so, run this command before installing MySQL using APT:

    Press CTRL+C to copy
    $> sudo debconf-set-selections <<< "mysql-server mysql-server/lowercase-table-names select Enabled"
    Note

    The ability to enable lower_case_table_names using debconf-set-selections was added in MySQL 8.0.17. Enabling lower_case_table_names sets the value to 1.

  • mandatory_roles

    Command-Line Format --mandatory-roles=value
    System Variable mandatory_roles
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type String
    Default Value empty string

    Roles the server should treat as mandatory. In effect, these roles are automatically granted to every user, although setting mandatory_roles does not actually change any user accounts, and the granted roles are not visible in the mysql.role_edges system table.

    The variable value is a comma-separated list of role names. Example:

    Press CTRL+C to copy
    SET PERSIST mandatory_roles = '`role1`@`%`,`role2`,role3,role4@localhost';

    Setting the runtime value of mandatory_roles requires the ROLE_ADMIN privilege, in addition to the SYSTEM_VARIABLES_ADMIN privilege (or the deprecated SUPER privilege) normally required to set a global system variable runtime value.

    Role names consist of a user part and host part in user_name@host_name format. The host part, if omitted, defaults to %. For additional information, see Section 6.2.5, 鈥淪pecifying Role Names鈥?/a>.

    The mandatory_roles value is a string, so user names and host names, if quoted, must be written in a fashion permitted for quoting within quoted strings.

    Roles named in the value of mandatory_roles cannot be revoked with REVOKE or dropped with DROP ROLE or DROP USER.

    To prevent sessions from being made system sessions by default, a role that has the SYSTEM_USER privilege cannot be listed in the value of the mandatory_roles system variable:

    Mandatory roles, like explicitly granted roles, do not take effect until activated (see Activating Roles). At login time, role activation occurs for all granted roles if the activate_all_roles_on_login system variable is enabled; otherwise, or for roles that are set as default roles otherwise. At runtime, SET ROLE activates roles.

    Roles that do not exist when assigned to mandatory_roles but are created later may require special treatment to be considered mandatory. For details, see Defining Mandatory Roles.

    SHOW GRANTS displays mandatory roles according to the rules described in Section 13.7.7.21, 鈥淪HOW GRANTS Statement鈥?/a>.

  • max_allowed_packet

    Command-Line Format --max-allowed-packet=#
    System Variable max_allowed_packet
    Scope Global, Session
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Integer
    Default Value 67108864
    Minimum Value 1024
    Maximum Value 1073741824
    Unit bytes
    Block Size 1024

    The maximum size of one packet or any generated/intermediate string, or any parameter sent by the mysql_stmt_send_long_data() C API function. The default is 64MB.

    The packet message buffer is initialized to net_buffer_length bytes, but can grow up to max_allowed_packet bytes when needed. This value by default is small, to catch large (possibly incorrect) packets.

    You must increase this value if you are using large BLOB columns or long strings. It should be as big as the largest BLOB you want to use. The protocol limit for max_allowed_packet is 1GB. The value should be a multiple of 1024; nonmultiples are rounded down to the nearest multiple.

    When you change the message buffer size by changing the value of the max_allowed_packet variable, you should also change the buffer size on the client side if your client program permits it. The default max_allowed_packet value built in to the client library is 1GB, but individual client programs might override this. For example, mysql and mysqldump have defaults of 16MB and 24MB, respectively. They also enable you to change the client-side value by setting max_allowed_packet on the command line or in an option file.

    The session value of this variable is read only. The client can receive up to as many bytes as the session value. However, the server does not send to the client more bytes than the current global max_allowed_packet value. (The global value could be less than the session value if the global value is changed after the client connects.)

  • max_connect_errors

    Command-Line Format --max-connect-errors=#
    System Variable max_connect_errors
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Integer
    Default Value 100
    Minimum Value 1
    Maximum Value (64-bit platforms) 18446744073709551615
    Maximum Value (32-bit platforms) 4294967295

    After max_connect_errors successive connection requests from a host are interrupted without a successful connection, the server blocks that host from further connections. If a connection from a host is established successfully within fewer than max_connect_errors attempts after a previous connection was interrupted, the error count for the host is cleared to zero. To unblock blocked hosts, flush the host cache; see Flushing the Host Cache.

  • max_connections

    Command-Line Format --max-connections=#
    System Variable max_connections
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Integer
    Default Value 151
    Minimum Value 1
    Maximum Value 100000

    The maximum permitted number of simultaneous client connections. The maximum effective value is the lesser of the effective value of open_files_limit - 810, and the value actually set for max_connections.

    For more information, see Section 5.1.12.1, 鈥淐onnection Interfaces鈥?/a>.

  • max_delayed_threads

    Command-Line Format --max-delayed-threads=#
    Deprecated Yes
    System Variable max_delayed_threads
    Scope Global, Session
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Integer
    Default Value 20
    Minimum Value 0
    Maximum Value 16384

    This system variable is deprecated (because DELAYED inserts are not supported) and subject to removal in a future MySQL release.

    As of MySQL 8.0.27, setting the session value of this system variable is a restricted operation. The session user must have privileges sufficient to set restricted session variables. See Section 5.1.9.1, 鈥淪ystem Variable Privileges鈥?/a>.

  • max_digest_length

    Command-Line Format --max-digest-length=#
    System Variable max_digest_length
    Scope Global
    Dynamic No
    SET_VAR Hint Applies No
    Type Integer
    Default Value 1024
    Minimum Value 0
    Maximum Value 1048576
    Unit bytes

    The maximum number of bytes of memory reserved per session for computation of normalized statement digests. Once that amount of space is used during digest computation, truncation occurs: no further tokens from a parsed statement are collected or figure into its digest value. Statements that differ only after that many bytes of parsed tokens produce the same normalized statement digest and are considered identical if compared or if aggregated for digest statistics.

    Warning

    Setting max_digest_length to zero disables digest production, which also disables server functionality that requires digests, such as MySQL Enterprise Firewall.

    Decreasing the max_digest_length value reduces memory use but causes the digest value of more statements to become indistinguishable if they differ only at the end. Increasing the value permits longer statements to be distinguished but increases memory use, particularly for workloads that involve large numbers of simultaneous sessions (the server allocates max_digest_length bytes per session).

    The parser uses this system variable as a limit on the maximum length of normalized statement digests that it computes. The Performance Schema, if it tracks statement digests, makes a copy of the digest value, using the performance_schema_max_digest_length. system variable as a limit on the maximum length of digests that it stores. Consequently, if performance_schema_max_digest_length is less than max_digest_length, digest values stored in the Performance Schema are truncated relative to the original digest values.

    For more information about statement digesting, see Section 27.10, 鈥淧erformance Schema Statement Digests and Sampling鈥?/a>.

  • max_error_count

    Command-Line Format --max-error-count=#
    System Variable max_error_count
    Scope Global, Session
    Dynamic Yes
    SET_VAR Hint Applies Yes
    Type Integer
    Default Value 1024
    Minimum Value 0
    Maximum Value 65535

    The maximum number of error, warning, and information messages to be stored for display by the SHOW ERRORS and SHOW WARNINGS statements. This is the same as the number of condition areas in the diagnostics area, and thus the number of conditions that can be inspected by GET DIAGNOSTICS.

    As of MySQL 8.0.27, setting the session value of this system variable is a restricted operation. The session user must have privileges sufficient to set restricted session variables. See Section 5.1.9.1, 鈥淪ystem Variable Privileges鈥?/a>.

  • max_execution_time

    Command-Line Format --max-execution-time=#
    System Variable max_execution_time
    Scope Global, Session
    Dynamic Yes
    SET_VAR Hint Applies Yes
    Type Integer
    Default Value 0
    Minimum Value 0
    Maximum Value 4294967295
    Unit milliseconds

    The execution timeout for SELECT statements, in milliseconds. If the value is 0, timeouts are not enabled.

    max_execution_time applies as follows:

    • The global max_execution_time value provides the default for the session value for new connections. The session value applies to SELECT executions executed within the session that include no MAX_EXECUTION_TIME(N) optimizer hint or for which N is 0.

    • max_execution_time applies to read-only SELECT statements. Statements that are not read only are those that invoke a stored function that modifies data as a side effect.

    • max_execution_time is ignored for SELECT statements in stored programs.

  • max_heap_table_size

    Command-Line Format --max-heap-table-size=#
    System Variable max_heap_table_size
    Scope Global, Session
    Dynamic Yes
    SET_VAR Hint Applies Yes
    Type Integer
    Default Value 16777216
    Minimum Value 16384
    Maximum Value (64-bit platforms) 18446744073709550592
    Maximum Value (32-bit platforms) 4294966272
    Unit bytes
    Block Size 1024

    This variable sets the maximum size to which user-created MEMORY tables are permitted to grow. The value of the variable is used to calculate MEMORY table MAX_ROWS values.

    The block size is 1024. A value that is not an exact multiple of the block size is rounded down to the next lower multiple of the block size by MySQL Server before storing the value for the system variable. The parser allows values up to the maximum unsigned integer value for the platform (4294967295 or 232鈭? for a 32-bit system, 18446744073709551615 or 264鈭? for a 64-bit system) but the actual maximum is a block size lower.

    Setting this variable has no effect on any existing MEMORY table, unless the table is re-created with a statement such as CREATE TABLE or altered with ALTER TABLE or TRUNCATE TABLE. A server restart also sets the maximum size of existing MEMORY tables to the global max_heap_table_size value.

    This variable is also used in conjunction with tmp_table_size to limit the size of internal in-memory tables. See Section 8.4.4, 鈥淚nternal Temporary Table Use in MySQL鈥?/a>.

    max_heap_table_size is not replicated. See Section 17.5.1.21, 鈥淩eplication and MEMORY Tables鈥?/a>, and Section 17.5.1.39, 鈥淩eplication and Variables鈥?/a>, for more information.

  • max_insert_delayed_threads

    Deprecated Yes
    System Variable max_insert_delayed_threads
    Scope Global, Session
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Integer
    Default Value 0
    Minimum Value 20
    Maximum Value 16384

    This variable is a synonym for max_delayed_threads. Like max_delayed_threads, it is deprecated (because DELAYED inserts are not supported) and subject to removal in a future MySQL release.

    As of MySQL 8.0.27, setting the session value of this system variable is a restricted operation. The session user must have privileges sufficient to set restricted session variables. See Section 5.1.9.1, 鈥淪ystem Variable Privileges鈥?/a>.

  • max_join_size

    Command-Line Format --max-join-size=#
    System Variable max_join_size
    Scope Global, Session
    Dynamic Yes
    SET_VAR Hint Applies Yes
    Type Integer
    Default Value 18446744073709551615
    Minimum Value 1
    Maximum Value 18446744073709551615

    As of MySQL 8.0.31, this represents a limit on the maximum number of row accesses in base tables made by a join. If the server's estimate indicates that a greater number of rows than max_join_size must be read from the base tables, the statement is rejected with an error.

    MySQL 8.0.30 and earlier: Do not permit statements that probably need to examine more than max_join_size rows (for single-table statements) or row combinations (for multiple-table statements) or that are likely to do more than max_join_size disk seeks. By setting this value, you can catch statements where keys are not used properly and that would probably take a long time. Set it if your users tend to perform joins that lack a WHERE clause, that take a long time, or that return millions of rows. For more information, see Using Safe-Updates Mode (--safe-updates).

    Regardless of MySQL release version, setting this variable to a value other than DEFAULT resets the value of sql_big_selects to 0. If you set the sql_big_selects value again, the max_join_size variable is ignored.

  • max_length_for_sort_data

    Command-Line Format --max-length-for-sort-data=#
    Deprecated 8.0.20
    System Variable max_length_for_sort_data
    Scope Global, Session
    Dynamic Yes
    SET_VAR Hint Applies Yes
    Type Integer
    Default Value 4096
    Minimum Value 4
    Maximum Value 8388608
    Unit bytes

    This variable is deprecated as of MySQL 8.0.20 due to optimizer changes that make it obsolete and of no effect. Previously, it acted as the cutoff on the size of index values that determines which filesort algorithm to use. See Section 8.2.1.16, 鈥淥RDER BY Optimization鈥?/a>.

  • max_points_in_geometry

    Command-Line Format --max-points-in-geometry=#
    System Variable max_points_in_geometry
    Scope Global, Session
    Dynamic Yes
    SET_VAR Hint Applies Yes
    Type Integer
    Default Value 65536
    Minimum Value 3
    Maximum Value 1048576

    The maximum value of the points_per_circle argument to the ST_Buffer_Strategy() function.

  • max_prepared_stmt_count

    Command-Line Format --max-prepared-stmt-count=#
    System Variable max_prepared_stmt_count
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Integer
    Default Value 16382
    Minimum Value 0
    Maximum Value (鈮?8.0.18) 4194304
    Maximum Value (鈮?8.0.17) 1048576

    This variable limits the total number of prepared statements in the server. It can be used in environments where there is the potential for denial-of-service attacks based on running the server out of memory by preparing huge numbers of statements. If the value is set lower than the current number of prepared statements, existing statements are not affected and can be used, but no new statements can be prepared until the current number drops below the limit. Setting the value to 0 disables prepared statements.

  • max_seeks_for_key

    Command-Line Format --max-seeks-for-key=#
    System Variable max_seeks_for_key
    Scope Global, Session
    Dynamic Yes
    SET_VAR Hint Applies Yes
    Type Integer
    Default Value (Windows) 4294967295
    Default Value (Other, 64-bit platforms) 18446744073709551615
    Default Value (Other, 32-bit platforms) 4294967295
    Minimum Value 1
    Maximum Value (Windows) 4294967295
    Maximum Value (Other, 64-bit platforms) 18446744073709551615
    Maximum Value (Other, 32-bit platforms) 4294967295

    Limit the assumed maximum number of seeks when looking up rows based on a key. The MySQL optimizer assumes that no more than this number of key seeks are required when searching for matching rows in a table by scanning an index, regardless of the actual cardinality of the index (see Section 13.7.7.22, 鈥淪HOW INDEX Statement鈥?/a>). By setting this to a low value (say, 100), you can force MySQL to prefer indexes instead of table scans.

  • max_sort_length

    Command-Line Format --max-sort-length=#
    System Variable max_sort_length
    Scope Global, Session
    Dynamic Yes
    SET_VAR Hint Applies Yes
    Type Integer
    Default Value 1024
    Minimum Value 4
    Maximum Value 8388608
    Unit bytes

    The number of bytes to use when sorting string values which use PAD SPACE collations. The server uses only the first max_sort_length bytes of any such value and ignores the rest. Consequently, such values that differ only after the first max_sort_length bytes compare as equal for GROUP BY, ORDER BY, and DISTINCT operations. (This behavior differs from previous versions of MySQL, where this setting was applied to all values used in comparisons.)

    Increasing the value of max_sort_length may require increasing the value of sort_buffer_size as well. For details, see Section 8.2.1.16, 鈥淥RDER BY Optimization鈥?/a>

  • max_sp_recursion_depth

    Command-Line Format --max-sp-recursion-depth[=#]
    System Variable max_sp_recursion_depth
    Scope Global, Session
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Integer
    Default Value 0
    Minimum Value 0
    Maximum Value 255

    The number of times that any given stored procedure may be called recursively. The default value for this option is 0, which completely disables recursion in stored procedures. The maximum value is 255.

    Stored procedure recursion increases the demand on thread stack space. If you increase the value of max_sp_recursion_depth, it may be necessary to increase thread stack size by increasing the value of thread_stack at server startup.

  • max_user_connections

    Command-Line Format --max-user-connections=#
    System Variable max_user_connections
    Scope Global, Session
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Integer
    Default Value 0
    Minimum Value 0
    Maximum Value 4294967295

    The maximum number of simultaneous connections permitted to any given MySQL user account. A value of 0 (the default) means 鈥?span class="quote">no limit.鈥?/span>

    This variable has a global value that can be set at server startup or runtime. It also has a read-only session value that indicates the effective simultaneous-connection limit that applies to the account associated with the current session. The session value is initialized as follows:

    • If the user account has a nonzero MAX_USER_CONNECTIONS resource limit, the session max_user_connections value is set to that limit.

    • Otherwise, the session max_user_connections value is set to the global value.

    Account resource limits are specified using the CREATE USER or ALTER USER statement. See Section 6.2.21, 鈥淪etting Account Resource Limits鈥?/a>.

  • max_write_lock_count

    Command-Line Format --max-write-lock-count=#
    System Variable max_write_lock_count
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Integer
    Default Value (Windows) 4294967295
    Default Value (Other, 64-bit platforms) 18446744073709551615
    Default Value (Other, 32-bit platforms) 4294967295
    Minimum Value 1
    Maximum Value (Windows) 4294967295
    Maximum Value (Other, 64-bit platforms) 18446744073709551615
    Maximum Value (Other, 32-bit platforms) 4294967295

    After this many write locks, permit some pending read lock requests to be processed in between. Write lock requests have higher priority than read lock requests. However, if max_write_lock_count is set to some low value (say, 10), read lock requests may be preferred over pending write lock requests if the read lock requests have already been passed over in favor of 10 write lock requests. Normally this behavior does not occur because max_write_lock_count by default has a very large value.

  • mecab_rc_file

    Command-Line Format --mecab-rc-file=file_name
    System Variable mecab_rc_file
    Scope Global
    Dynamic No
    SET_VAR Hint Applies No
    Type File name

    The mecab_rc_file option is used when setting up the MeCab full-text parser.

    The mecab_rc_file option defines the path to the mecabrc configuration file, which is the configuration file for MeCab. The option is read-only and can only be set at startup. The mecabrc configuration file is required to initialize MeCab.

    For information about the MeCab full-text parser, see Section 12.10.9, 鈥淢eCab Full-Text Parser Plugin鈥?/a>.

    For information about options that can be specified in the MeCab mecabrc configuration file, refer to the MeCab Documentation on the Google Developers site.

  • metadata_locks_cache_size

    Command-Line Format --metadata-locks-cache-size=#
    Deprecated Yes (removed in 8.0.13)
    System Variable metadata_locks_cache_size
    Scope Global
    Dynamic No
    SET_VAR Hint Applies No
    Type Integer
    Default Value 1024
    Minimum Value 1
    Maximum Value 1048576
    Unit bytes

    This system variable was removed in MySQL 8.0.13.

  • metadata_locks_hash_instances

    Command-Line Format --metadata-locks-hash-instances=#
    Deprecated Yes (removed in 8.0.13)
    System Variable metadata_locks_hash_instances
    Scope Global
    Dynamic No
    SET_VAR Hint Applies No
    Type Integer
    Default Value 8
    Minimum Value 1
    Maximum Value 1024

    This system variable was removed in MySQL 8.0.13.

  • min_examined_row_limit

    Command-Line Format --min-examined-row-limit=#
    System Variable min_examined_row_limit
    Scope Global, Session
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Integer
    Default Value 0
    Minimum Value 0
    Maximum Value (64-bit platforms) 18446744073709551615
    Maximum Value (32-bit platforms) 4294967295

    Queries that examine fewer than this number of rows are not logged to the slow query log.

    As of MySQL 8.0.27, setting the session value of this system variable is a restricted operation. The session user must have privileges sufficient to set restricted session variables. See Section 5.1.9.1, 鈥淪ystem Variable Privileges鈥?/a>.

  • myisam_data_pointer_size

    Command-Line Format --myisam-data-pointer-size=#
    System Variable myisam_data_pointer_size
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Integer
    Default Value 6
    Minimum Value 2
    Maximum Value 7
    Unit bytes

    The default pointer size in bytes, to be used by CREATE TABLE for MyISAM tables when no MAX_ROWS option is specified. This variable cannot be less than 2 or larger than 7. The default value is 6. See Section B.3.2.10, 鈥淭he table is full鈥?/a>.

  • myisam_max_sort_file_size

    Command-Line Format --myisam-max-sort-file-size=#
    System Variable myisam_max_sort_file_size
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Integer
    Default Value (Windows) 2146435072
    Default Value (Other, 64-bit platforms) 9223372036853727232
    Default Value (Other, 32-bit platforms) 2147483648
    Minimum Value 0
    Maximum Value (Windows) 2146435072
    Maximum Value (Other, 64-bit platforms) 9223372036853727232
    Maximum Value (Other, 32-bit platforms) 2147483648
    Unit bytes

    The maximum size of the temporary file that MySQL is permitted to use while re-creating a MyISAM index (during REPAIR TABLE, ALTER TABLE, or LOAD DATA). If the file size would be larger than this value, the index is created using the key cache instead, which is slower. The value is given in bytes.

    If MyISAM index files exceed this size and disk space is available, increasing the value may help performance. The space must be available in the file system containing the directory where the original index file is located.

  • myisam_mmap_size

    Command-Line Format --myisam-mmap-size=#
    System Variable myisam_mmap_size
    Scope Global
    Dynamic No
    SET_VAR Hint Applies No
    Type Integer
    Default Value (64-bit platforms) 18446744073709551615
    Default Value (32-bit platforms) 4294967295
    Minimum Value 7
    Maximum Value (64-bit platforms) 18446744073709551615
    Maximum Value (32-bit platforms) 4294967295
    Unit bytes

    The maximum amount of memory to use for memory mapping compressed MyISAM files. If many compressed MyISAM tables are used, the value can be decreased to reduce the likelihood of memory-swapping problems.

  • myisam_recover_options

    Command-Line Format --myisam-recover-options[=list]
    System Variable myisam_recover_options
    Scope Global
    Dynamic No
    SET_VAR Hint Applies No
    Type Enumeration
    Default Value OFF
    Valid Values

    OFF

    DEFAULT

    BACKUP

    FORCE

    QUICK

    Set the MyISAM storage engine recovery mode. The variable value is any combination of the values of OFF, DEFAULT, BACKUP, FORCE, or QUICK. If you specify multiple values, separate them by commas. Specifying the variable with no value at server startup is the same as specifying DEFAULT, and specifying with an explicit value of "" disables recovery (same as a value of OFF). If recovery is enabled, each time mysqld opens a MyISAM table, it checks whether the table is marked as crashed or was not closed properly. (The last option works only if you are running with external locking disabled.) If this is the case, mysqld runs a check on the table. If the table was corrupted, mysqld attempts to repair it.

    The following options affect how the repair works.

    Option Description
    OFF No recovery.
    DEFAULT Recovery without backup, forcing, or quick checking.
    BACKUP If the data file was changed during recovery, save a backup of the tbl_name.MYD file as tbl_name-datetime.BAK.
    FORCE Run recovery even if we would lose more than one row from the .MYD file.
    QUICK Do not check the rows in the table if there are not any delete blocks.

    Before the server automatically repairs a table, it writes a note about the repair to the error log. If you want to be able to recover from most problems without user intervention, you should use the options BACKUP,FORCE. This forces a repair of a table even if some rows would be deleted, but it keeps the old data file as a backup so that you can later examine what happened.

    See Section 16.2.1, 鈥淢yISAM Startup Options鈥?/a>.

  • myisam_repair_threads

    Command-Line Format --myisam-repair-threads=#
    Deprecated 8.0.29 (removed in 8.0.30)
    System Variable myisam_repair_threads
    Scope Global, Session
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Integer
    Default Value 1
    Minimum Value 1
    Maximum Value (64-bit platforms) 18446744073709551615
    Maximum Value (32-bit platforms) 4294967295
    Note

    This system variable is deprecated in MySQL 8.0.29 and removed in MySQL 8.0.30.

    From MySQL 8.0.29, values other than 1 produce a warning.

    If this value is greater than 1, MyISAM table indexes are created in parallel (each index in its own thread) during the Repair by sorting process. The default value is 1.

    Note

    Multithreaded repair is beta-quality code.

  • myisam_sort_buffer_size

    Command-Line Format --myisam-sort-buffer-size=#
    System Variable myisam_sort_buffer_size
    Scope Global, Session
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Integer
    Default Value 8388608
    Minimum Value 4096
    Maximum Value (64-bit platforms) 18446744073709551615
    Maximum Value (32-bit platforms) 4294967295
    Unit bytes

    The size of the buffer that is allocated when sorting MyISAM indexes during a REPAIR TABLE or when creating indexes with CREATE INDEX or ALTER TABLE.

  • myisam_stats_method

    Command-Line Format --myisam-stats-method=name
    System Variable myisam_stats_method
    Scope Global, Session
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Enumeration
    Default Value nulls_unequal
    Valid Values

    nulls_unequal

    nulls_equal

    nulls_ignored

    How the server treats NULL values when collecting statistics about the distribution of index values for MyISAM tables. This variable has three possible values, nulls_equal, nulls_unequal, and nulls_ignored. For nulls_equal, all NULL index values are considered equal and form a single value group that has a size equal to the number of NULL values. For nulls_unequal, NULL values are considered unequal, and each NULL forms a distinct value group of size 1. For nulls_ignored, NULL values are ignored.

    The method that is used for generating table statistics influences how the optimizer chooses indexes for query execution, as described in Section 8.3.8, 鈥淚nnoDB and MyISAM Index Statistics Collection鈥?/a>.

  • myisam_use_mmap

    Command-Line Format --myisam-use-mmap[={OFF|ON}]
    System Variable myisam_use_mmap
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Boolean
    Default Value OFF

    Use memory mapping for reading and writing MyISAM tables.

  • mysql_native_password_proxy_users

    Command-Line Format --mysql-native-password-proxy-users[={OFF|ON}]
    System Variable mysql_native_password_proxy_users
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Boolean
    Default Value OFF

    This variable controls whether the mysql_native_password built-in authentication plugin supports proxy users. It has no effect unless the check_proxy_users system variable is enabled. For information about user proxying, see Section 6.2.19, 鈥淧roxy Users鈥?/a>.

  • named_pipe

    Command-Line Format --named-pipe[={OFF|ON}]
    System Variable named_pipe
    Scope Global
    Dynamic No
    SET_VAR Hint Applies No
    Platform Specific Windows
    Type Boolean
    Default Value OFF

    (Windows only.) Indicates whether the server supports connections over named pipes.

  • named_pipe_full_access_group

    Command-Line Format --named-pipe-full-access-group=value
    Introduced 8.0.14
    System Variable named_pipe_full_access_group
    Scope Global
    Dynamic No
    SET_VAR Hint Applies No
    Platform Specific Windows
    Type String
    Default Value empty string
    Valid Values

    empty string

    valid Windows local group name

    *everyone*

    (Windows only.) The access control granted to clients on the named pipe created by the MySQL server is set to the minimum necessary for successful communication when the named_pipe system variable is enabled to support named-pipe connections. Some MySQL client software can open named pipe connections without any additional configuration; however, other client software may still require full access to open a named pipe connection.

    This variable sets the name of a Windows local group whose members are granted sufficient access by the MySQL server to use named-pipe clients. As of MySQL 8.0.24, the default value is set to an empty string, which means that no Windows user is granted full access to the named pipe.

    A new Windows local group name (for example, mysql_access_client_users) can be created in Windows and then used to replace the default value when access is absolutely necessary. In this case, limit the membership of the group to as few users as possible, removing users from the group when their client software is upgraded. A non-member of the group who attempts to open a connection to MySQL with the affected named-pipe client is denied access until a Windows administrator adds the user to the group. Newly added users must log out and log in again to join the group (required by Windows).

    Setting the value to '*everyone*' provides a language-independent way of referring to the Everyone group on Windows. The Everyone group is not secure by default.

  • net_buffer_length

    Command-Line Format --net-buffer-length=#
    System Variable net_buffer_length
    Scope Global, Session
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Integer
    Default Value 16384
    Minimum Value 1024
    Maximum Value 1048576
    Unit bytes
    Block Size 1024

    Each client thread is associated with a connection buffer and result buffer. Both begin with a size given by net_buffer_length but are dynamically enlarged up to max_allowed_packet bytes as needed. The result buffer shrinks to net_buffer_length after each SQL statement.

    This variable should not normally be changed, but if you have very little memory, you can set it to the expected length of statements sent by clients. If statements exceed this length, the connection buffer is automatically enlarged. The maximum value to which net_buffer_length can be set is 1MB.

    The session value of this variable is read only.

  • net_read_timeout

    Command-Line Format --net-read-timeout=#
    System Variable net_read_timeout
    Scope Global, Session
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Integer
    Default Value 30
    Minimum Value 1
    Maximum Value 31536000
    Unit seconds

    The number of seconds to wait for more data from a connection before aborting the read. When the server is reading from the client, net_read_timeout is the timeout value controlling when to abort. When the server is writing to the client, net_write_timeout is the timeout value controlling when to abort. See also replica_net_timeout and slave_net_timeout.

  • net_retry_count

    Command-Line Format --net-retry-count=#
    System Variable net_retry_count
    Scope Global, Session
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Integer
    Default Value 10
    Minimum Value 1
    Maximum Value (64-bit platforms) 18446744073709551615
    Maximum Value (32-bit platforms) 4294967295

    If a read or write on a communication port is interrupted, retry this many times before giving up. This value should be set quite high on FreeBSD because internal interrupts are sent to all threads.

  • net_write_timeout

    Command-Line Format --net-write-timeout=#
    System Variable net_write_timeout
    Scope Global, Session
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Integer
    Default Value 60
    Minimum Value 1
    Maximum Value 31536000
    Unit seconds

    The number of seconds to wait for a block to be written to a connection before aborting the write. See also net_read_timeout.

  • new

    Command-Line Format --new[={OFF|ON}]
    System Variable new
    Scope Global, Session
    Dynamic Yes
    SET_VAR Hint Applies No
    Disabled by skip-new
    Type Boolean
    Default Value OFF

    This variable was used in MySQL 4.0 to turn on some 4.1 behaviors, and is retained for backward compatibility. Its value is always OFF.

    In NDB Cluster, setting this variable to ON makes it possible to employ partitioning types other than KEY or LINEAR KEY with NDB tables. This feature is experimental only, and not supported in production. For additional information, see User-defined partitioning and the NDB storage engine (NDB Cluster).

  • ngram_token_size

    Command-Line Format --ngram-token-size=#
    System Variable ngram_token_size
    Scope Global
    Dynamic No
    SET_VAR Hint Applies No
    Type Integer
    Default Value 2
    Minimum Value 1
    Maximum Value 10

    Defines the n-gram token size for the n-gram full-text parser. The ngram_token_size option is read-only and can only be modified at startup. The default value is 2 (bigram). The maximum value is 10.

    For more information about how to configure this variable, see Section 12.10.8, 鈥渘gram Full-Text Parser鈥?/a>.

  • offline_mode

    Command-Line Format --offline-mode[={OFF|ON}]
    System Variable offline_mode
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Boolean
    Default Value OFF

    In offline mode, the MySQL instance disconnects client users unless they have relevant privileges, and does not allow them to initiate new connections. Clients that are refused access receive an ER_SERVER_OFFLINE_MODE error.

    To put a server in offline mode, change the value of the offline_mode system variable from OFF to ON. To resume normal operations, change offline_mode from ON to OFF. To control offline mode, an administrator account must have the SYSTEM_VARIABLES_ADMIN privilege and the CONNECTION_ADMIN privilege (or the deprecated SUPER privilege, which covers both these privileges). CONNECTION_ADMIN is required from MySQL 8.0.31 and recommended in all releases to prevent accidental lockout.

    Offline mode has these characteristics:

    • Connected client users who do not have the CONNECTION_ADMIN privilege (or the deprecated SUPER privilege) are disconnected on the next request, with an appropriate error. Disconnection includes terminating running statements and releasing locks. Such clients also cannot initiate new connections, and receive an appropriate error.

    • Connected client users who have the CONNECTION_ADMIN or SUPER privilege are not disconnected, and can initiate new connections to manage the server.

    • From MySQL 8.0.30, if the user that puts a server in offline mode does not have the SYSTEM_USER privilege, connected client users who have the SYSTEM_USER privilege are also not disconnected. However, these users cannot initiate new connections to the server while it is in offline mode, unless they have the CONNECTION_ADMIN or SUPER privilege as well. It is only their existing connection that cannot be terminated, because the SYSTEM_USER privilege is required to kill a session or statement that is executing with the SYSTEM_USER privilege.

    • Replication threads are permitted to keep applying data to the server.

  • old

    Command-Line Format --old[={OFF|ON}]
    System Variable old
    Scope Global
    Dynamic No
    SET_VAR Hint Applies No
    Type Boolean
    Default Value OFF

    old is a compatibility variable. It is disabled by default, but can be enabled at startup to revert the server to behaviors present in older versions.

    When old is enabled, it changes the default scope of index hints to that used prior to MySQL 5.1.17. That is, index hints with no FOR clause apply only to how indexes are used for row retrieval and not to resolution of ORDER BY or GROUP BY clauses. (See Section 8.9.4, 鈥淚ndex Hints鈥?/a>.) Take care about enabling this in a replication setup. With statement-based binary logging, having different modes for the source and replicas might lead to replication errors.

  • old_alter_table

    Command-Line Format --old-alter-table[={OFF|ON}]
    System Variable old_alter_table
    Scope Global, Session
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Boolean
    Default Value OFF

    When this variable is enabled, the server does not use the optimized method of processing an ALTER TABLE operation. It reverts to using a temporary table, copying over the data, and then renaming the temporary table to the original, as used by MySQL 5.0 and earlier. For more information on the operation of ALTER TABLE, see Section 13.1.9, 鈥淎LTER TABLE Statement鈥?/a>.

    ALTER TABLE ... DROP PARTITION with old_alter_table=ON rebuilds the partitioned table and attempts to move data from the dropped partition to another partition with a compatible PARTITION ... VALUES definition. Data that cannot be moved to another partition is deleted. In earlier releases, ALTER TABLE ... DROP PARTITION with old_alter_table=ON deletes data stored in the partition and drops the partition.

  • open_files_limit

    Command-Line Format --open-files-limit=#
    System Variable open_files_limit
    Scope Global
    Dynamic No
    SET_VAR Hint Applies No
    Type Integer
    Default Value 5000, with possible adjustment
    Minimum Value 0
    Maximum Value platform dependent

    The number of file descriptors available to mysqld from the operating system:

    • At startup, mysqld reserves descriptors with setrlimit(), using the value requested at by setting this variable directly or by using the --open-files-limit option to mysqld_safe. If mysqld produces the error Too many open files, try increasing the open_files_limit value. Internally, the maximum value for this variable is the maximum unsigned integer value, but the actual maximum is platform dependent.

    • At runtime, the value of open_files_limit indicates the number of file descriptors actually permitted to mysqld by the operating system, which might differ from the value requested at startup. If the number of file descriptors requested during startup cannot be allocated, mysqld writes a warning to the error log.

    The effective open_files_limit value is based on the value specified at system startup (if any) and the values of max_connections and table_open_cache, using these formulas:

    • 10 + max_connections + (table_open_cache * 2). Using the defaults for these variables yields 8161.

      On Windows only, 2048 (the value of the C Run-Time Library file descriptor maximum) is added to this number. This totals 10209, again using the default values for the indicated system variables.

    • max_connections * 5

    • MySQL 8.0.19 and higher: The operating system limit.

    • Prior to MySQL 8.0.19:

      • The operating system limit if that limit is positive but not Infinity.

      • If the operating system limit is Infinity: open_files_limit value if specified at startup, 5000 if not.

    The server attempts to obtain the number of file descriptors using the maximum of those values, capped to the maximum unsigned integer value. If that many descriptors cannot be obtained, the server attempts to obtain as many as the system permits.

    The effective value is 0 on systems where MySQL cannot change the number of open files.

    On Unix, the value cannot be set greater than the value displayed by the ulimit -n command. On Linux systems using systemd, the value cannot be set greater than LimitNOFILE (this is DefaultLimitNOFILE, if LimitNOFILE is not set); otherwise, on Linux, the value of open_files_limit cannot exceed ulimit -n.

  • optimizer_prune_level

    Command-Line Format --optimizer-prune-level=#
    System Variable optimizer_prune_level
    Scope Global, Session
    Dynamic Yes
    SET_VAR Hint Applies Yes
    Type Integer
    Default Value 1
    Minimum Value 0
    Maximum Value 1

    Controls the heuristics applied during query optimization to prune less-promising partial plans from the optimizer search space. A value of 0 disables heuristics so that the optimizer performs an exhaustive search. A value of 1 causes the optimizer to prune plans based on the number of rows retrieved by intermediate plans.

  • optimizer_search_depth

    Command-Line Format --optimizer-search-depth=#
    System Variable optimizer_search_depth
    Scope Global, Session
    Dynamic Yes
    SET_VAR Hint Applies Yes
    Type Integer
    Default Value 62
    Minimum Value 0
    Maximum Value 62

    The maximum depth of search performed by the query optimizer. Values larger than the number of relations in a query result in better query plans, but take longer to generate an execution plan for a query. Values smaller than the number of relations in a query return an execution plan quicker, but the resulting plan may be far from being optimal. If set to 0, the system automatically picks a reasonable value.

  • optimizer_switch

    Command-Line Format --optimizer-switch=value
    System Variable optimizer_switch
    Scope Global, Session
    Dynamic Yes
    SET_VAR Hint Applies Yes
    Type Set
    Valid Values (鈮?8.0.22)

    batched_key_access={on|off}

    block_nested_loop={on|off}

    condition_fanout_filter={on|off}

    derived_condition_pushdown={on|off}

    derived_merge={on|off}

    duplicateweedout={on|off}

    engine_condition_pushdown={on|off}

    firstmatch={on|off}

    hash_join={on|off}

    index_condition_pushdown={on|off}

    index_merge={on|off}

    index_merge_intersection={on|off}

    index_merge_sort_union={on|off}

    index_merge_union={on|off}

    loosescan={on|off}

    materialization={on|off}

    mrr={on|off}

    mrr_cost_based={on|off}

    prefer_ordering_index={on|off}

    semijoin={on|off}

    skip_scan={on|off}

    subquery_materialization_cost_based={on|off}

    subquery_to_derived={on|off}

    use_index_extensions={on|off}

    use_invisible_indexes={on|off}

    Valid Values (鈮?8.0.21)

    batched_key_access={on|off}

    block_nested_loop={on|off}

    condition_fanout_filter={on|off}

    derived_merge={on|off}

    duplicateweedout={on|off}

    engine_condition_pushdown={on|off}

    firstmatch={on|off}

    hash_join={on|off}

    index_condition_pushdown={on|off}

    index_merge={on|off}

    index_merge_intersection={on|off}

    index_merge_sort_union={on|off}

    index_merge_union={on|off}

    loosescan={on|off}

    materialization={on|off}

    mrr={on|off}

    mrr_cost_based={on|off}

    prefer_ordering_index={on|off}

    semijoin={on|off}

    skip_scan={on|off}

    subquery_materialization_cost_based={on|off}

    subquery_to_derived={on|off}

    use_index_extensions={on|off}

    use_invisible_indexes={on|off}

    Valid Values (鈮?8.0.18)

    batched_key_access={on|off}

    block_nested_loop={on|off}

    condition_fanout_filter={on|off}

    derived_merge={on|off}

    duplicateweedout={on|off}

    engine_condition_pushdown={on|off}

    firstmatch={on|off}

    hash_join={on|off}

    index_condition_pushdown={on|off}

    index_merge={on|off}

    index_merge_intersection={on|off}

    index_merge_sort_union={on|off}

    index_merge_union={on|off}

    loosescan={on|off}

    materialization={on|off}

    mrr={on|off}

    mrr_cost_based={on|off}

    semijoin={on|off}

    skip_scan={on|off}

    subquery_materialization_cost_based={on|off}

    use_index_extensions={on|off}

    use_invisible_indexes={on|off}

    Valid Values (鈮?8.0.13)

    batched_key_access={on|off}

    block_nested_loop={on|off}

    condition_fanout_filter={on|off}

    derived_merge={on|off}

    duplicateweedout={on|off}

    engine_condition_pushdown={on|off}

    firstmatch={on|off}

    index_condition_pushdown={on|off}

    index_merge={on|off}

    index_merge_intersection={on|off}

    index_merge_sort_union={on|off}

    index_merge_union={on|off}

    loosescan={on|off}

    materialization={on|off}

    mrr={on|off}

    mrr_cost_based={on|off}

    semijoin={on|off}

    skip_scan={on|off}

    subquery_materialization_cost_based={on|off}

    use_index_extensions={on|off}

    use_invisible_indexes={on|off}

    Valid Values (鈮?8.0.12)

    batched_key_access={on|off}

    block_nested_loop={on|off}

    condition_fanout_filter={on|off}

    derived_merge={on|off}

    duplicateweedout={on|off}

    engine_condition_pushdown={on|off}

    firstmatch={on|off}

    index_condition_pushdown={on|off}

    index_merge={on|off}

    index_merge_intersection={on|off}

    index_merge_sort_union={on|off}

    index_merge_union={on|off}

    loosescan={on|off}

    materialization={on|off}

    mrr={on|off}

    mrr_cost_based={on|off}

    semijoin={on|off}

    subquery_materialization_cost_based={on|off}

    use_index_extensions={on|off}

    use_invisible_indexes={on|off}

    The optimizer_switch system variable enables control over optimizer behavior. The value of this variable is a set of flags, each of which has a value of on or off to indicate whether the corresponding optimizer behavior is enabled or disabled. This variable has global and session values and can be changed at runtime. The global default can be set at server startup.

    To see the current set of optimizer flags, select the variable value:

    Press CTRL+C to copy
    mysql> SELECT @@optimizer_switch\G *************************** 1. row *************************** @@optimizer_switch: index_merge=on,index_merge_union=on, index_merge_sort_union=on,index_merge_intersection=on, engine_condition_pushdown=on,index_condition_pushdown=on, mrr=on,mrr_cost_based=on,block_nested_loop=on, batched_key_access=off,materialization=on,semijoin=on, loosescan=on,firstmatch=on,duplicateweedout=on, subquery_materialization_cost_based=on, use_index_extensions=on,condition_fanout_filter=on, derived_merge=on,use_invisible_indexes=off,skip_scan=on, hash_join=on,subquery_to_derived=off, prefer_ordering_index=on,hypergraph_optimizer=off, derived_condition_pushdown=on

    For more information about the syntax of this variable and the optimizer behaviors that it controls, see Section 8.9.2, 鈥淪witchable Optimizations鈥?/a>.

  • optimizer_trace

    Command-Line Format --optimizer-trace=value
    System Variable optimizer_trace
    Scope Global, Session
    Dynamic Yes
    SET_VAR Hint Applies No
    Type String

    This variable controls optimizer tracing. For details, see MySQL Internals: Tracing the Optimizer.

  • optimizer_trace_features

    Command-Line Format --optimizer-trace-features=value
    System Variable optimizer_trace_features
    Scope Global, Session
    Dynamic Yes
    SET_VAR Hint Applies No
    Type String

    This variable enables or disables selected optimizer tracing features. For details, see MySQL Internals: Tracing the Optimizer.

  • optimizer_trace_limit

    Command-Line Format --optimizer-trace-limit=#
    System Variable optimizer_trace_limit
    Scope Global, Session
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Integer
    Default Value 1
    Minimum Value 0
    Maximum Value 2147483647

    The maximum number of optimizer traces to display. For details, see MySQL Internals: Tracing the Optimizer.

  • optimizer_trace_max_mem_size

    Command-Line Format --optimizer-trace-max-mem-size=#
    System Variable optimizer_trace_max_mem_size
    Scope Global, Session
    Dynamic Yes
    SET_VAR Hint Applies Yes
    Type Integer
    Default Value 1048576
    Minimum Value 0
    Maximum Value 4294967295
    Unit bytes

    The maximum cumulative size of stored optimizer traces. For details, see MySQL Internals: Tracing the Optimizer.

  • optimizer_trace_offset

    Command-Line Format --optimizer-trace-offset=#
    System Variable optimizer_trace_offset
    Scope Global, Session
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Integer
    Default Value -1
    Minimum Value -2147483647
    Maximum Value 2147483647

    The offset of optimizer traces to display. For details, see MySQL Internals: Tracing the Optimizer.

  • performance_schema_xxx

    Performance Schema system variables are listed in Section 27.15, 鈥淧erformance Schema System Variables鈥?/a>. These variables may be used to configure Performance Schema operation.

  • parser_max_mem_size

    Command-Line Format --parser-max-mem-size=#
    System Variable parser_max_mem_size
    Scope Global, Session
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Integer
    Default Value (64-bit platforms) 18446744073709551615
    Default Value (32-bit platforms) 4294967295
    Minimum Value 10000000
    Maximum Value (64-bit platforms) 18446744073709551615
    Maximum Value (32-bit platforms) 4294967295
    Unit bytes

    The maximum amount of memory available to the parser. The default value places no limit on memory available. The value can be reduced to protect against out-of-memory situations caused by parsing long or complex SQL statements.

  • partial_revokes

    Command-Line Format --partial-revokes[={OFF|ON}]
    Introduced 8.0.16
    System Variable partial_revokes
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Boolean
    Default Value

    OFF (if partial revokes do not exist)

    ON (if partial revokes exist)

    Enabling this variable makes it possible to revoke privileges partially. Specifically, for users who have privileges at the global level, partial_revokes enables privileges for specific schemas to be revoked while leaving the privileges in place for other schemas. For example, a user who has the global UPDATE privilege can be restricted from exercising this privilege on the mysql system schema. (Or, stated another way, the user is enabled to exercise the UPDATE privilege on all schemas except the mysql schema.) In this sense, the user's global UPDATE privilege is partially revoked.

    Once enabled, partial_revokes cannot be disabled if any account has privilege restrictions. If any such account exists, disabling partial_revokes fails:

    To disable partial_revokes in this case, first modify each account that has partially revoked privileges, either by re-granting the privileges or by removing the account.

    Note

    In privilege assignments, enabling partial_revokes causes MySQL to interpret occurrences of unescaped _ and % SQL wildcard characters in schema names as literal characters, just as if they had been escaped as \_ and \%. Because this changes how MySQL interprets privileges, it may be advisable to avoid unescaped wildcard characters in privilege assignments for installations where partial_revokes may be enabled.

    For more information, including instructions for removing partial revokes, see Section 6.2.12, 鈥淧rivilege Restriction Using Partial Revokes鈥?/a>.

  • password_history

    Command-Line Format --password-history=#
    System Variable password_history
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Integer
    Default Value 0
    Minimum Value 0
    Maximum Value 4294967295

    This variable defines the global policy for controlling reuse of previous passwords based on required minimum number of password changes. For an account password used previously, this variable indicates the number of subsequent account password changes that must occur before the password can be reused. If the value is 0 (the default), there is no reuse restriction based on number of password changes.

    Changes to this variable apply immediately to all accounts defined with the PASSWORD HISTORY DEFAULT option.

    The global number-of-changes password reuse policy can be overridden as desired for individual accounts using the PASSWORD HISTORY option of the CREATE USER and ALTER USER statements. See Section 6.2.15, 鈥淧assword Management鈥?/a>.

  • password_require_current

    Command-Line Format --password-require-current[={OFF|ON}]
    Introduced 8.0.13
    System Variable password_require_current
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Boolean
    Default Value OFF

    This variable defines the global policy for controlling whether attempts to change an account password must specify the current password to be replaced.

    Changes to this variable apply immediately to all accounts defined with the PASSWORD REQUIRE CURRENT DEFAULT option.

    The global verification-required policy can be overridden as desired for individual accounts using the PASSWORD REQUIRE option of the CREATE USER and ALTER USER statements. See Section 6.2.15, 鈥淧assword Management鈥?/a>.

  • password_reuse_interval

    Command-Line Format --password-reuse-interval=#
    System Variable password_reuse_interval
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Integer
    Default Value 0
    Minimum Value 0
    Maximum Value 4294967295
    Unit days

    This variable defines the global policy for controlling reuse of previous passwords based on time elapsed. For an account password used previously, this variable indicates the number of days that must pass before the password can be reused. If the value is 0 (the default), there is no reuse restriction based on time elapsed.

    Changes to this variable apply immediately to all accounts defined with the PASSWORD REUSE INTERVAL DEFAULT option.

    The global time-elapsed password reuse policy can be overridden as desired for individual accounts using the PASSWORD REUSE INTERVAL option of the CREATE USER and ALTER USER statements. See Section 6.2.15, 鈥淧assword Management鈥?/a>.

  • persisted_globals_load

    Command-Line Format --persisted-globals-load[={OFF|ON}]
    System Variable persisted_globals_load
    Scope Global
    Dynamic No
    SET_VAR Hint Applies No
    Type Boolean
    Default Value ON

    Whether to load persisted configuration settings from the mysqld-auto.cnf file in the data directory. The server normally processes this file at startup after all other option files (see Section 4.2.2.2, 鈥淯sing Option Files鈥?/a>). Disabling persisted_globals_load causes the server startup sequence to skip mysqld-auto.cnf.

    To modify the contents of mysqld-auto.cnf, use the SET PERSIST, SET PERSIST_ONLY, and RESET PERSIST statements. See Section 5.1.9.3, 鈥淧ersisted System Variables鈥?/a>.

  • persist_only_admin_x509_subject

    Command-Line Format --persist-only-admin-x509-subject=string
    Introduced 8.0.14
    System Variable persist_only_admin_x509_subject
    Scope Global
    Dynamic No
    SET_VAR Hint Applies No
    Type String
    Default Value empty string

    SET PERSIST and SET PERSIST_ONLY enable system variables to be persisted to the mysqld-auto.cnf option file in the data directory (see Section 13.7.6.1, 鈥淪ET Syntax for Variable Assignment鈥?/a>). Persisting system variables enables runtime configuration changes that affect subsequent server restarts, which is convenient for remote administration not requiring direct access to MySQL server host option files. However, some system variables are nonpersistible or can be persisted only under certain restrictive conditions.

    The persist_only_admin_x509_subject system variable specifies the SSL certificate X.509 Subject value that users must have to be able to persist system variables that are persist-restricted. The default value is the empty string, which disables the Subject check so that persist-restricted system variables cannot be persisted by any user.

    If persist_only_admin_x509_subject is nonempty, users who connect to the server using an encrypted connection and supply an SSL certificate with the designated Subject value then can use SET PERSIST_ONLY to persist persist-restricted system variables. For information about persist-restricted system variables and instructions for configuring MySQL to enable persist_only_admin_x509_subject, see Section 5.1.9.4, 鈥淣onpersistible and Persist-Restricted System Variables鈥?/a>.

  • persist_sensitive_variables_in_plaintext

    Command-Line Format --persist_sensitive_variables_in_plaintext[={OFF|ON}]
    Introduced 8.0.29
    System Variable persist_sensitive_variables_in_plaintext
    Scope Global
    Dynamic No
    SET_VAR Hint Applies No
    Type Boolean
    Default Value ON

    persist_sensitive_variables_in_plaintext controls whether the server is permitted to store the values of sensitive system variables in an unencrypted format, if keyring component support is not available at the time when SET PERSIST is used to set the value of the system variable. It also controls whether or not the server can start if the encrypted values cannot be decrypted. Note that keyring plugins do not support secure storage of sensitive system variables; a keyring component (see Section 6.4.4, 鈥淭he MySQL Keyring鈥?/a>) must be enabled on the MySQL Server instance to support secure storage.

    The default setting, ON, encrypts the values if keyring component support is available, and persists them unencrypted (with a warning) if it is not. The next time any persisted system variable is set, if keyring support is available at that time, the server encrypts the values of any unencrypted sensitive system variables. The ON setting also allows the server to start if encrypted system variable values cannot be decrypted, in which case a warning is issued and the default values for the system variables are used. In that situation, their values cannot be changed until they can be decrypted.

    The most secure setting, OFF, means sensitive system variable values cannot be persisted if keyring component support is unavailable. The OFF setting also means the server does not start if encrypted system variable values cannot be decrypted.

    For more information, see Persisting Sensitive System Variables.

  • pid_file

    Command-Line Format --pid-file=file_name
    System Variable pid_file
    Scope Global
    Dynamic No
    SET_VAR Hint Applies No
    Type File name

    The path name of the file in which the server writes its process ID. The server creates the file in the data directory unless an absolute path name is given to specify a different directory. If you specify this variable, you must specify a value. If you do not specify this variable, MySQL uses a default value of host_name.pid, where host_name is the name of the host machine.

    The process ID file is used by other programs such as mysqld_safe to determine the server's process ID. On Windows, this variable also affects the default error log file name. See Section 5.4.2, 鈥淭he Error Log鈥?/a>.

  • plugin_dir

    Command-Line Format --plugin-dir=dir_name
    System Variable plugin_dir
    Scope Global
    Dynamic No
    SET_VAR Hint Applies No
    Type Directory name
    Default Value BASEDIR/lib/plugin

    The path name of the plugin directory.

    If the plugin directory is writable by the server, it may be possible for a user to write executable code to a file in the directory using SELECT ... INTO DUMPFILE. This can be prevented by making plugin_dir read only to the server or by setting secure_file_priv to a directory where SELECT writes can be made safely.

  • port

    Command-Line Format --port=port_num
    System Variable port
    Scope Global
    Dynamic No
    SET_VAR Hint Applies No
    Type Integer
    Default Value 3306
    Minimum Value 0
    Maximum Value 65535

    The number of the port on which the server listens for TCP/IP connections. This variable can be set with the --port option.

  • preload_buffer_size

    Command-Line Format --preload-buffer-size=#
    System Variable preload_buffer_size
    Scope Global, Session
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Integer
    Default Value 32768
    Minimum Value 1024
    Maximum Value 1073741824
    Unit bytes

    The size of the buffer that is allocated when preloading indexes.

    As of MySQL 8.0.27, setting the session value of this system variable is a restricted operation. The session user must have privileges sufficient to set restricted session variables. See Section 5.1.9.1, 鈥淪ystem Variable Privileges鈥?/a>.

  • print_identified_with_as_hex

    Command-Line Format --print-identified-with-as-hex[={OFF|ON}]
    Introduced 8.0.17
    System Variable print_identified_with_as_hex
    Scope Global, Session
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Boolean
    Default Value OFF

    Password hash values displayed in the IDENTIFIED WITH clause of output from SHOW CREATE USER may contain unprintable characters that have adverse effects on terminal displays and in other environments. Enabling print_identified_with_as_hex causes SHOW CREATE USER to display such hash values as hexadecimal strings rather than as regular string literals. Hash values that do not contain unprintable characters still display as regular string literals, even with this variable enabled.

  • profiling

    If set to 0 or OFF (the default), statement profiling is disabled. If set to 1 or ON, statement profiling is enabled and the SHOW PROFILE and SHOW PROFILES statements provide access to profiling information. See Section 13.7.7.31, 鈥淪HOW PROFILES Statement鈥?/a>.

    This variable is deprecated; expect it to be removed in a future MySQL release.

  • profiling_history_size

    The number of statements for which to maintain profiling information if profiling is enabled. The default value is 15. The maximum value is 100. Setting the value to 0 effectively disables profiling. See Section 13.7.7.31, 鈥淪HOW PROFILES Statement鈥?/a>.

    This variable is deprecated; expect it to be removed in a future MySQL release.

  • protocol_compression_algorithms

    Command-Line Format --protocol-compression-algorithms=value
    Introduced 8.0.18
    System Variable protocol_compression_algorithms
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Set
    Default Value zlib,zstd,uncompressed
    Valid Values

    zlib

    zstd

    uncompressed

    The compression algorithms that the server permits for incoming connections. These include connections by client programs and by servers participating in source/replica replication or Group Replication. Compression does not apply to connections for FEDERATED tables.

    protocol_compression_algorithms does not control connection compression for X Protocol. See Section 20.5.5, 鈥淐onnection Compression with X Plugin鈥?/a> for information on how this operates.

    The variable value is a list of one or more comma-separated compression algorithm names, in any order, chosen from the following items (not case-sensitive):

    The default value of zlib,zstd,uncompressed indicates that the server permits all compression algorithms.

    For more information, see Section 4.2.8, 鈥淐onnection Compression Control鈥?/a>.

  • protocol_version

    System Variable protocol_version
    Scope Global
    Dynamic No
    SET_VAR Hint Applies No
    Type Integer
    Default Value 10
    Minimum Value 0
    Maximum Value 4294967295

    The version of the client/server protocol used by the MySQL server.

  • proxy_user

    System Variable proxy_user
    Scope Session
    Dynamic No
    SET_VAR Hint Applies No
    Type String

    If the current client is a proxy for another user, this variable is the proxy user account name. Otherwise, this variable is NULL. See Section 6.2.19, 鈥淧roxy Users鈥?/a>.

  • pseudo_replica_mode

    Introduced 8.0.26
    System Variable pseudo_replica_mode
    Scope Session
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Boolean

    From MySQL 8.0.26, pseudo_replica_mode is used in place of pseudo_slave_mode, which is deprecated from that release. The operation and effects are the same, only the terminology has changed.

    pseudo_replica_mode is for internal server use. It assists with the correct handling of transactions that originated on older or newer servers than the server currently processing them. mysqlbinlog sets the value of pseudo_replica_mode to true before executing any SQL statements.

    Setting the session value of pseudo_replica_mode is a restricted operation. The session user must have either the REPLICATION_APPLIER privilege (see Section 17.3.3, 鈥淩eplication Privilege Checks鈥?/a>), or privileges sufficient to set restricted session variables (see Section 5.1.9.1, 鈥淪ystem Variable Privileges鈥?/a>). However, note that the variable is not intended for users to set; it is set automatically by the replication infrastructure.

    pseudo_replica_mode has the following effects on the handling of prepared XA transactions, which can be attached to or detached from the handling session (by default, the session that issues XA START):

    • If true, and the handling session has executed an internal-use BINLOG statement, XA transactions are automatically detached from the session as soon as the first part of the transaction up to XA PREPARE finishes, so they can be committed or rolled back by any session that has the XA_RECOVER_ADMIN privilege.

    • If false, XA transactions remain attached to the handling session as long as that session is alive, during which time no other session can commit the transaction. The prepared transaction is only detached if the session disconnects or the server restarts.

    pseudo_replica_mode has the following effects on the original_commit_timestamp replication delay timestamp and the original_server_version system variable:

    • If true, transactions that do not explicitly set original_commit_timestamp or original_server_version are assumed to originate on another, unknown server, so the value 0, meaning unknown, is assigned to both the timestamp and the system variable.

    • If false, transactions that do not explicitly set original_commit_timestamp or original_server_version are assumed to originate on the current server, so the current timestamp and the current server's version are assigned to the timestamp and the system variable.

    In MySQL 8.0.14 and later, pseudo_replica_mode has the following effects on the handling of a statement that sets one or more unsupported (removed or unknown) SQL modes:

    • If true, the server ignores the unsupported mode and raises a warning.

    • If false, the server rejects the statement with ER_UNSUPPORTED_SQL_MODE.

  • pseudo_slave_mode

    Deprecated 8.0.26
    System Variable pseudo_slave_mode
    Scope Session
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Boolean

    From MySQL 8.0.26, pseudo_slave_mode is deprecated and the alias pseudo_replica_mode is used instead. pseudo_slave_mode is for internal server use. It assists with the correct handling of transactions that originated on older or newer servers than the server currently processing them. mysqlbinlog sets the value of pseudo_slave_mode to true before executing any SQL statements.

    Setting the session value of this system variable is a restricted operation. The session user must have either the REPLICATION_APPLIER privilege (see Section 17.3.3, 鈥淩eplication Privilege Checks鈥?/a>), or privileges sufficient to set restricted session variables (see Section 5.1.9.1, 鈥淪ystem Variable Privileges鈥?/a>). However, note that the variable is not intended for users to set; it is set automatically by the replication infrastructure.

    See the description of the pseudo_replica_mode system variable for the effects of pseudo_slave_mode.

  • pseudo_thread_id

    System Variable pseudo_thread_id
    Scope Session
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Integer
    Default Value 2147483647
    Minimum Value 0
    Maximum Value 2147483647

    This variable is for internal server use.

    Warning

    Changing the session value of the pseudo_thread_id system variable changes the value returned by the CONNECTION_ID() function.

    As of MySQL 8.0.14, setting the session value of this system variable is a restricted operation. The session user must have privileges sufficient to set restricted session variables. See Section 5.1.9.1, 鈥淪ystem Variable Privileges鈥?/a>.

  • query_alloc_block_size

    Command-Line Format --query-alloc-block-size=#
    System Variable query_alloc_block_size
    Scope Global, Session
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Integer
    Default Value 8192
    Minimum Value 1024
    Maximum Value 4294966272
    Unit bytes
    Block Size 1024

    The allocation size in bytes of memory blocks that are allocated for objects created during statement parsing and execution. If you have problems with memory fragmentation, it might help to increase this parameter.

    The block size for the byte number is 1024. A value that is not an exact multiple of the block size is rounded down to the next lower multiple of the block size by MySQL Server before storing the value for the system variable. The parser allows values up to the maximum unsigned integer value for the platform (4294967295 or 232鈭? for a 32-bit system, 18446744073709551615 or 264鈭? for a 64-bit system) but the actual maximum is a block size lower.

  • query_prealloc_size

    Command-Line Format --query-prealloc-size=#
    Deprecated 8.0.29
    System Variable query_prealloc_size
    Scope Global, Session
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Integer
    Default Value 8192
    Minimum Value 8192
    Maximum Value (64-bit platforms) 18446744073709550592
    Maximum Value (32-bit platforms) 4294966272
    Unit bytes
    Block Size 1024

    MySQL 8.0.28 and earlier: This sets the size in bytes of the persistent buffer used for statement parsing and execution. This buffer is not freed between statements. If you are running complex queries, a larger query_prealloc_size value might be helpful in improving performance, because it can reduce the need for the server to perform memory allocation during query execution operations. You should be aware that doing this does not necessarily eliminate allocation completely; the server may still allocate memory in some situations, such as for operations relating to transactions, or to stored programs.

    As of MySQL 8.0.29, query_prealloc_size is deprecated, and setting it no longer has any effect; you should expect its removal in a future release of MySQL.

    The block size is 1024. A value that is not an exact multiple of the block size is rounded down to the next lower multiple of the block size by MySQL Server before storing the value for the system variable. The parser allows values up to the maximum unsigned integer value for the platform (4294967295 or 232鈭? for a 32-bit system, 18446744073709551615 or 264鈭? for a 64-bit system) but the actual maximum is a block size lower.

  • rand_seed1

    System Variable rand_seed1
    Scope Session
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Integer
    Default Value N/A
    Minimum Value 0
    Maximum Value 4294967295

    The rand_seed1 and rand_seed2 variables exist as session variables only, and can be set but not read. The variables鈥攂ut not their values鈥攁re shown in the output of SHOW VARIABLES.

    The purpose of these variables is to support replication of the RAND() function. For statements that invoke RAND(), the source passes two values to the replica, where they are used to seed the random number generator. The replica uses these values to set the session variables rand_seed1 and rand_seed2 so that RAND() on the replica generates the same value as on the source.

  • rand_seed2

    See the description for rand_seed1.

  • range_alloc_block_size

    Command-Line Format --range-alloc-block-size=#
    System Variable range_alloc_block_size
    Scope Global, Session
    Dynamic Yes
    SET_VAR Hint Applies Yes
    Type Integer
    Default Value 4096
    Minimum Value 4096
    Maximum Value (64-bit platforms) 18446744073709550592
    Maximum Value 4294966272
    Unit bytes
    Block Size 1024

    The size in bytes of blocks that are allocated when doing range optimization.

    The block size for the byte number is 1024. A value that is not an exact multiple of the block size is rounded down to the next lower multiple of the block size by MySQL Server before storing the value for the system variable. The parser allows values up to the maximum unsigned integer value for the platform (4294967295 or 232鈭? for a 32-bit system, 18446744073709551615 or 264鈭? for a 64-bit system) but the actual maximum is a block size lower.

  • range_optimizer_max_mem_size

    Command-Line Format --range-optimizer-max-mem-size=#
    System Variable range_optimizer_max_mem_size
    Scope Global, Session
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Integer
    Default Value 8388608
    Minimum Value 0
    Maximum Value 18446744073709551615
    Unit bytes

    The limit on memory consumption for the range optimizer. A value of 0 means 鈥?span class="quote">no limit.鈥?/span> If an execution plan considered by the optimizer uses the range access method but the optimizer estimates that the amount of memory needed for this method would exceed the limit, it abandons the plan and considers other plans. For more information, see Limiting Memory Use for Range Optimization.

  • rbr_exec_mode

    System Variable rbr_exec_mode
    Scope Session
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Enumeration
    Default Value STRICT
    Valid Values

    STRICT

    IDEMPOTENT

    For internal use by mysqlbinlog. This variable switches the server between IDEMPOTENT mode and STRICT mode. IDEMPOTENT mode causes suppression of duplicate-key and no-key-found errors in BINLOG statements generated by mysqlbinlog. This mode is useful when replaying a row-based binary log on a server that causes conflicts with existing data. mysqlbinlog sets this mode when you specify the --idempotent option by writing the following to the output:

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    SET SESSION RBR_EXEC_MODE=IDEMPOTENT;

    As of MySQL 8.0.18, setting the session value of this system variable is no longer a restricted operation.

  • read_buffer_size

    Command-Line Format --read-buffer-size=#
    System Variable read_buffer_size
    Scope Global, Session
    Dynamic Yes
    SET_VAR Hint Applies Yes
    Type Integer
    Default Value 131072
    Minimum Value 8192
    Maximum Value 2147479552
    Unit bytes
    Block Size 4096

    Each thread that does a sequential scan for a MyISAM table allocates a buffer of this size (in bytes) for each table it scans. If you do many sequential scans, you might want to increase this value, which defaults to 131072. The value of this variable should be a multiple of 4KB. If it is set to a value that is not a multiple of 4KB, its value is rounded down to the nearest multiple of 4KB.

    This option is also used in the following context for all storage engines:

    • For caching the indexes in a temporary file (not a temporary table), when sorting rows for ORDER BY.

    • For bulk insert into partitions.

    • For caching results of nested queries.

    read_buffer_size is also used in one other storage engine-specific way: to determine the memory block size for MEMORY tables.

    Beginning with MySQL 8.0.22, the value of select_into_buffer_size is used in place of the value of read_buffer_size for the buffer used when executing SELECT INTO DUMPFILE and SELECT INTO OUTFILE statements.

    For more information about memory use during different operations, see Section 8.12.3.1, 鈥淗ow MySQL Uses Memory鈥?/a>.

  • read_only

    Command-Line Format --read-only[={OFF|ON}]
    System Variable read_only
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Boolean
    Default Value OFF

    If the read_only system variable is enabled, the server permits no client updates except from users who have the CONNECTION_ADMIN privilege (or the deprecated SUPER privilege). This variable is disabled by default.

    The server also supports a super_read_only system variable (disabled by default), which has these effects:

    When read_only is enabled and when super_read_only is enabled, the server still permits these operations:

    Changes to read_only on a replication source server are not replicated to replica servers. The value can be set on a replica independent of the setting on the source.

    The following conditions apply to attempts to enable read_only (including implicit attempts resulting from enabling super_read_only):

    • The attempt fails and an error occurs if you have any explicit locks (acquired with LOCK TABLES) or have a pending transaction.

    • The attempt blocks while other clients have any ongoing statement, active LOCK TABLES WRITE, or ongoing commit, until the locks are released and the statements and transactions end. While the attempt to enable read_only is pending, requests by other clients for table locks or to begin transactions also block until read_only has been set.

    • The attempt blocks if there are active transactions that hold metadata locks, until those transactions end.

    • read_only can be enabled while you hold a global read lock (acquired with FLUSH TABLES WITH READ LOCK) because that does not involve table locks.

  • read_rnd_buffer_size

    Command-Line Format --read-rnd-buffer-size=#
    System Variable read_rnd_buffer_size
    Scope Global, Session
    Dynamic Yes
    SET_VAR Hint Applies Yes
    Type Integer
    Default Value 262144
    Minimum Value 1
    Maximum Value 2147483647
    Unit bytes

    This variable is used for reads from MyISAM tables, and, for any storage engine, for Multi-Range Read optimization.

    When reading rows from a MyISAM table in sorted order following a key-sorting operation, the rows are read through this buffer to avoid disk seeks. See Section 8.2.1.16, 鈥淥RDER BY Optimization鈥?/a>. Setting the variable to a large value can improve ORDER BY performance by a lot. However, this is a buffer allocated for each client, so you should not set the global variable to a large value. Instead, change the session variable only from within those clients that need to run large queries.

    For more information about memory use during different operations, see Section 8.12.3.1, 鈥淗ow MySQL Uses Memory鈥?/a>. For information about Multi-Range Read optimization, see Section 8.2.1.11, 鈥淢ulti-Range Read Optimization鈥?/a>.

  • regexp_stack_limit

    Command-Line Format --regexp-stack-limit=#
    System Variable regexp_stack_limit
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Integer
    Default Value 8000000
    Minimum Value 0
    Maximum Value 2147483647
    Unit bytes

    The maximum available memory in bytes for the internal stack used for regular expression matching operations performed by REGEXP_LIKE() and similar functions (see Section 12.8.2, 鈥淩egular Expressions鈥?/a>).

  • regexp_time_limit

    Command-Line Format --regexp-time-limit=#
    System Variable regexp_time_limit
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Integer
    Default Value 32
    Minimum Value 0
    Maximum Value 2147483647

    The time limit for regular expression matching operations performed by REGEXP_LIKE() and similar functions (see Section 12.8.2, 鈥淩egular Expressions鈥?/a>). This limit is expressed as the maximum permitted number of steps performed by the match engine, and thus affects execution time only indirectly. Typically, it is on the order of milliseconds.

  • require_row_format

    Introduced 8.0.19
    System Variable require_row_format
    Scope Session
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Boolean
    Default Value OFF

    This variable is for internal server use by replication and mysqlbinlog. It restricts DML events executed in the session to events encoded in row-based binary logging format only, and temporary tables cannot be created. Queries that do not respect the restrictions fail.

    Setting the session value of this system variable to ON requires no privileges. Setting the session value of this system variable to OFF is a restricted operation, and the session user must have privileges sufficient to set restricted session variables. See Section 5.1.9.1, 鈥淪ystem Variable Privileges鈥?/a>.

  • require_secure_transport

    Command-Line Format --require-secure-transport[={OFF|ON}]
    System Variable require_secure_transport
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Boolean
    Default Value OFF

    Whether client connections to the server are required to use some form of secure transport. When this variable is enabled, the server permits only TCP/IP connections encrypted using TLS/SSL, or connections that use a socket file (on Unix) or shared memory (on Windows). The server rejects nonsecure connection attempts, which fail with an ER_SECURE_TRANSPORT_REQUIRED error.

    This capability supplements per-account SSL requirements, which take precedence. For example, if an account is defined with REQUIRE SSL, enabling require_secure_transport does not make it possible to use the account to connect using a Unix socket file.

    It is possible for a server to have no secure transports available. For example, a server on Windows supports no secure transports if started without specifying any SSL certificate or key files and with the shared_memory system variable disabled. Under these conditions, attempts to enable require_secure_transport at startup cause the server to write a message to the error log and exit. Attempts to enable the variable at runtime fail with an ER_NO_SECURE_TRANSPORTS_CONFIGURED error.

    See also Configuring Encrypted Connections as Mandatory.

  • resultset_metadata

    System Variable resultset_metadata
    Scope Session
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Enumeration
    Default Value FULL
    Valid Values

    FULL

    NONE

    For connections for which metadata transfer is optional, the client sets the resultset_metadata system variable to control whether the server returns result set metadata. Permitted values are FULL (return all metadata; this is the default) and NONE (return no metadata).

    For connections that are not metadata-optional, setting resultset_metadata to NONE produces an error.

    For details about managing result set metadata transfer, see Optional Result Set Metadata.

  • secondary_engine_cost_threshold

    Introduced 8.0.16
    System Variable secondary_engine_cost_threshold
    Scope Session
    Dynamic Yes
    SET_VAR Hint Applies Yes
    Type Numeric
    Default Value 100000.000000
    Minimum Value 0
    Maximum Value DBL_MAX (maximum double value)

    The optimizer cost threshold for query offload to a secondary engine.

    For use with HeatWave. See MySQL HeatWave User Guide.

  • schema_definition_cache

    Command-Line Format --schema-definition-cache=#
    System Variable schema_definition_cache
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Integer
    Default Value 256
    Minimum Value 256
    Maximum Value 524288

    Defines a limit for the number of schema definition objects, both used and unused, that can be kept in the dictionary object cache.

    Unused schema definition objects are only kept in the dictionary object cache when the number in use is less than the capacity defined by schema_definition_cache.

    A setting of 0 means that schema definition objects are only kept in the dictionary object cache while they are in use.

    For more information, see Section 14.4, 鈥淒ictionary Object Cache鈥?/a>.

  • secure_file_priv

    Command-Line Format --secure-file-priv=dir_name
    System Variable secure_file_priv
    Scope Global
    Dynamic No
    SET_VAR Hint Applies No
    Type String
    Default Value platform specific
    Valid Values

    empty string

    dirname

    NULL

    This variable is used to limit the effect of data import and export operations, such as those performed by the LOAD DATA and SELECT ... INTO OUTFILE statements and the LOAD_FILE() function. These operations are permitted only to users who have the FILE privilege.

    secure_file_priv may be set as follows:

    • If empty, the variable has no effect. This is not a secure setting.

    • If set to the name of a directory, the server limits import and export operations to work only with files in that directory. The directory must exist; the server does not create it.

    • If set to NULL, the server disables import and export operations.

    The default value is platform specific and depends on the value of the INSTALL_LAYOUT CMake option, as shown in the following table. To specify the default secure_file_priv value explicitly if you are building from source, use the INSTALL_SECURE_FILE_PRIVDIR CMake option.

    INSTALL_LAYOUT Value Default secure_file_priv Value
    STANDALONE empty
    DEB, RPM, SVR4 /var/lib/mysql-files
    Otherwise mysql-files under the CMAKE_INSTALL_PREFIX value

    The server checks the value of secure_file_priv at startup and writes a warning to the error log if the value is insecure. A non-NULL value is considered insecure if it is empty, or the value is the data directory or a subdirectory of it, or a directory that is accessible by all users. If secure_file_priv is set to a nonexistent path, the server writes an error message to the error log and exits.

  • select_into_buffer_size

    Command-Line Format --select-into-buffer-size=#
    Introduced 8.0.22
    System Variable select_into_buffer_size
    Scope Global, Session
    Dynamic Yes
    SET_VAR Hint Applies Yes
    Type Integer
    Default Value 131072
    Minimum Value 8192
    Maximum Value 2147479552
    Unit bytes
    Block Size 4096

    When using SELECT INTO OUTFILE or SELECT INTO DUMPFILE to dump data into one or more files for backup creation, data migration, or other purposes, writes can often be buffered and then trigger a large burst of write I/O activity to the disk or other storage device and stall other queries that are more sensitive to latency. You can use this variable to control the size of the buffer used to write data to the storage device to determine when buffer synchronization should occur, and thus to prevent write stalls of the kind just described from occurring.

    select_into_buffer_size overrides any value set for read_buffer_size. (select_into_buffer_size and read_buffer_size have the same default, maximum, and minimum values.) You can also use select_into_disk_sync_delay to set a timeout to be observed afterwards, each time synchronization takes place.

    As of MySQL 8.0.27, setting the session value of this system variable is a restricted operation. The session user must have privileges sufficient to set restricted session variables. See Section 5.1.9.1, 鈥淪ystem Variable Privileges鈥?/a>.

  • select_into_disk_sync

    Command-Line Format --select-into-disk-sync={ON|OFF}
    Introduced 8.0.22
    System Variable select_into_disk_sync
    Scope Global, Session
    Dynamic Yes
    SET_VAR Hint Applies Yes
    Type Boolean
    Default Value OFF
    Valid Values

    OFF

    ON

    When set on ON, enables buffer synchronization of writes to an output file by a long-running SELECT INTO OUTFILE or SELECT INTO DUMPFILE statement using select_into_buffer_size.

  • select_into_disk_sync_delay

    Command-Line Format --select-into-disk-sync-delay=#
    Introduced 8.0.22
    System Variable select_into_disk_sync_delay
    Scope Global, Session
    Dynamic Yes
    SET_VAR Hint Applies Yes
    Type Integer
    Default Value 0
    Minimum Value 0
    Maximum Value 31536000
    Unit milliseconds

    When buffer synchronization of writes to an output file by a long-running SELECT INTO OUTFILE or SELECT INTO DUMPFILE statement is enabled by select_into_disk_sync, this variable sets an optional delay (in milliseconds) following synchronization. 0 (the default) means no delay.

    As of MySQL 8.0.27, setting the session value of this system variable is a restricted operation. The session user must have privileges sufficient to set restricted session variables. See Section 5.1.9.1, 鈥淪ystem Variable Privileges鈥?/a>.

  • session_track_gtids

    Command-Line Format --session-track-gtids=value
    System Variable session_track_gtids
    Scope Global, Session
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Enumeration
    Default Value OFF
    Valid Values

    OFF

    OWN_GTID

    ALL_GTIDS

    Controls whether the server returns GTIDs to the client, enabling the client to use them to track the server state. Depending on the variable value, at the end of executing each transaction, the server鈥檚 GTIDs are captured and returned to the client as part of the acknowledgement. The possible values for session_track_gtids are as follows:

    • OFF: The server does not return GTIDs to the client. This is the default.

    • OWN_GTID: The server returns the GTIDs for all transactions that were successfully committed by this client in its current session since the last acknowledgement. Typically, this is the single GTID for the last transaction committed, but if a single client request resulted in multiple transactions, the server returns a GTID set containing all the relevant GTIDs.

    • ALL_GTIDS: The server returns the global value of its gtid_executed system variable, which it reads at a point after the transaction is successfully committed. As well as the GTID for the transaction just committed, this GTID set includes all transactions committed on the server by any client, and can include transactions committed after the point when the transaction currently being acknowledged was committed.

    session_track_gtids cannot be set within transactional context.

    For more information about session state tracking, see Section 5.1.18, 鈥淪erver Tracking of Client Session State鈥?/a>.

  • session_track_schema

    Command-Line Format --session-track-schema[={OFF|ON}]
    System Variable session_track_schema
    Scope Global, Session
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Boolean
    Default Value ON

    Controls whether the server tracks when the default schema (database) is set within the current session and notifies the client to make the schema name available.

    If the schema name tracker is enabled, name notification occurs each time the default schema is set, even if the new schema name is the same as the old.

    For more information about session state tracking, see Section 5.1.18, 鈥淪erver Tracking of Client Session State鈥?/a>.

  • session_track_state_change

    Command-Line Format --session-track-state-change[={OFF|ON}]
    System Variable session_track_state_change
    Scope Global, Session
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Boolean
    Default Value OFF

    Controls whether the server tracks changes to the state of the current session and notifies the client when state changes occur. Changes can be reported for these attributes of client session state:

    • The default schema (database).

    • Session-specific values for system variables.

    • User-defined variables.

    • Temporary tables.

    • Prepared statements.

    If the session state tracker is enabled, notification occurs for each change that involves tracked session attributes, even if the new attribute values are the same as the old. For example, setting a user-defined variable to its current value results in a notification.

    The session_track_state_change variable controls only notification of when changes occur, not what the changes are. For example, state-change notifications occur when the default schema is set or tracked session system variables are assigned, but the notification does not include the schema name or variable values. To receive notification of the schema name or session system variable values, use the session_track_schema or session_track_system_variables system variable, respectively.

    Note

    Assigning a value to session_track_state_change itself is not considered a state change and is not reported as such. However, if its name listed in the value of session_track_system_variables, any assignments to it do result in notification of the new value.

    For more information about session state tracking, see Section 5.1.18, 鈥淪erver Tracking of Client Session State鈥?/a>.

  • session_track_system_variables

    Command-Line Format --session-track-system-variables=#
    System Variable session_track_system_variables
    Scope Global, Session
    Dynamic Yes
    SET_VAR Hint Applies No
    Type String
    Default Value time_zone, autocommit, character_set_client, character_set_results, character_set_connection

    Controls whether the server tracks assignments to session system variables and notifies the client of the name and value of each assigned variable. The variable value is a comma-separated list of variables for which to track assignments. By default, notification is enabled for time_zone, autocommit, character_set_client, character_set_results, and character_set_connection. (The latter three variables are those affected by SET NAMES.)

    The special value * causes the server to track assignments to all session variables. If given, this value must be specified by itself without specific system variable names.

    To disable notification of session variable assignments, set session_track_system_variables to the empty string.

    If session system variable tracking is enabled, notification occurs for all assignments to tracked session variables, even if the new values are the same as the old.

    For more information about session state tracking, see Section 5.1.18, 鈥淪erver Tracking of Client Session State鈥?/a>.

  • session_track_transaction_info

    Command-Line Format --session-track-transaction-info=value
    System Variable session_track_transaction_info
    Scope Global, Session
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Enumeration
    Default Value OFF
    Valid Values

    OFF

    STATE

    CHARACTERISTICS

    Controls whether the server tracks the state and characteristics of transactions within the current session and notifies the client to make this information available. These session_track_transaction_info values are permitted:

    • OFF: Disable transaction state tracking. This is the default.

    • STATE: Enable transaction state tracking without characteristics tracking. State tracking enables the client to determine whether a transaction is in progress and whether it could be moved to a different session without being rolled back.

    • CHARACTERISTICS: Enable transaction state tracking, including characteristics tracking. Characteristics tracking enables the client to determine how to restart a transaction in another session so that it has the same characteristics as in the original session. The following characteristics are relevant for this purpose:

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      ISOLATION LEVEL READ ONLY READ WRITE WITH CONSISTENT SNAPSHOT

    For a client to safely relocate a transaction to another session, it must track not only transaction state but also transaction characteristics. In addition, the client must track the transaction_isolation and transaction_read_only system variables to correctly determine the session defaults. (To track these variables, list them in the value of the session_track_system_variables system variable.)

    For more information about session state tracking, see Section 5.1.18, 鈥淪erver Tracking of Client Session State鈥?/a>.

  • sha256_password_auto_generate_rsa_keys

    Command-Line Format --sha256-password-auto-generate-rsa-keys[={OFF|ON}]
    System Variable sha256_password_auto_generate_rsa_keys
    Scope Global
    Dynamic No
    SET_VAR Hint Applies No
    Type Boolean
    Default Value ON

    The server uses this variable to determine whether to autogenerate RSA private/public key-pair files in the data directory if they do not already exist.

    At startup, the server automatically generates RSA private/public key-pair files in the data directory if all of these conditions are true: The sha256_password_auto_generate_rsa_keys or caching_sha2_password_auto_generate_rsa_keys system variable is enabled; no RSA options are specified; the RSA files are missing from the data directory. These key-pair files enable secure password exchange using RSA over unencrypted connections for accounts authenticated by the sha256_password or caching_sha2_password plugin; see Section 6.4.1.3, 鈥淪HA-256 Pluggable Authentication鈥?/a>, and Section 6.4.1.2, 鈥淐aching SHA-2 Pluggable Authentication鈥?/a>.

    For more information about RSA file autogeneration, including file names and characteristics, see Section 6.3.3.1, 鈥淐reating SSL and RSA Certificates and Keys using MySQL鈥?/a>

    The auto_generate_certs system variable is related but controls autogeneration of SSL certificate and key files needed for secure connections using SSL.

  • sha256_password_private_key_path

    Command-Line Format --sha256-password-private-key-path=file_name
    System Variable sha256_password_private_key_path
    Scope Global
    Dynamic No
    SET_VAR Hint Applies No
    Type File name
    Default Value private_key.pem

    The value of this variable is the path name of the RSA private key file for the sha256_password authentication plugin. If the file is named as a relative path, it is interpreted relative to the server data directory. The file must be in PEM format.

    Important

    Because this file stores a private key, its access mode should be restricted so that only the MySQL server can read it.

    For information about sha256_password, see Section 6.4.1.3, 鈥淪HA-256 Pluggable Authentication鈥?/a>.

  • sha256_password_proxy_users

    Command-Line Format --sha256-password-proxy-users[={OFF|ON}]
    System Variable sha256_password_proxy_users
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Boolean
    Default Value OFF

    This variable controls whether the sha256_password built-in authentication plugin supports proxy users. It has no effect unless the check_proxy_users system variable is enabled. For information about user proxying, see Section 6.2.19, 鈥淧roxy Users鈥?/a>.

  • sha256_password_public_key_path

    Command-Line Format --sha256-password-public-key-path=file_name
    System Variable sha256_password_public_key_path
    Scope Global
    Dynamic No
    SET_VAR Hint Applies No
    Type File name
    Default Value public_key.pem

    The value of this variable is the path name of the RSA public key file for the sha256_password authentication plugin. If the file is named as a relative path, it is interpreted relative to the server data directory. The file must be in PEM format. Because this file stores a public key, copies can be freely distributed to client users. (Clients that explicitly specify a public key when connecting to the server using RSA password encryption must use the same public key as that used by the server.)

    For information about sha256_password, including information about how clients specify the RSA public key, see Section 6.4.1.3, 鈥淪HA-256 Pluggable Authentication鈥?/a>.

  • shared_memory

    Command-Line Format --shared-memory[={OFF|ON}]
    System Variable shared_memory
    Scope Global
    Dynamic No
    SET_VAR Hint Applies No
    Platform Specific Windows
    Type Boolean
    Default Value OFF

    (Windows only.) Whether the server permits shared-memory connections.

  • shared_memory_base_name

    Command-Line Format --shared-memory-base-name=name
    System Variable shared_memory_base_name
    Scope Global
    Dynamic No
    SET_VAR Hint Applies No
    Platform Specific Windows
    Type String
    Default Value MYSQL

    (Windows only.) The name of shared memory to use for shared-memory connections. This is useful when running multiple MySQL instances on a single physical machine. The default name is MYSQL. The name is case-sensitive.

    This variable applies only if the server is started with the shared_memory system variable enabled to support shared-memory connections.

  • show_create_table_skip_secondary_engine

    Command-Line Format --show-create-table-skip-secondary-engine[={OFF|ON}]
    Introduced 8.0.18
    System Variable show_create_table_skip_secondary_engine
    Scope Session
    Dynamic Yes
    SET_VAR Hint Applies Yes
    Type Boolean
    Default Value OFF

    Enabling show_create_table_skip_secondary_engine causes the SECONDARY ENGINE clause to be excluded from SHOW CREATE TABLE output, and from CREATE TABLE statements dumped by the mysqldump utility.

    mysqldump provides the --show-create-skip-secondary-engine option. When specified, it enables the show_create_table_skip_secondary_engine system variable for the duration of the dump operation.

    Attempting a mysqldump operation with the --show-create-skip-secondary-engine option on a release prior to MySQL 8.0.18 that does not support the show_create_table_skip_secondary_engine variable causes an error.

    For use with HeatWave. See MySQL HeatWave User Guide.

  • show_create_table_verbosity

    Command-Line Format --show-create-table-verbosity[={OFF|ON}]
    System Variable show_create_table_verbosity
    Scope Global, Session
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Boolean
    Default Value OFF

    SHOW CREATE TABLE normally does not show the ROW_FORMAT table option if the row format is the default format. Enabling this variable causes SHOW CREATE TABLE to display ROW_FORMAT regardless of whether it is the default format.

  • show_gipk_in_create_table_and_information_schema

    Command-Line Format --show-gipk-in-create-table-and-information-schema[={OFF|ON}]
    Introduced 8.0.30
    System Variable show_gipk_in_create_table_and_information_schema
    Scope Global, Session
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Boolean
    Default Value ON

    Whether generated invisible primary keys are visible in the output of SHOW statements and in Information Schema tables. When this variable is set to OFF, such keys are not shown.

    This variable is not replicated.

    For more information, see Section 13.1.20.11, 鈥淕enerated Invisible Primary Keys鈥?/a>.

  • show_old_temporals

    Command-Line Format --show-old-temporals[={OFF|ON}]
    Deprecated Yes
    System Variable show_old_temporals
    Scope Global, Session
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Boolean
    Default Value OFF

    Whether SHOW CREATE TABLE output includes comments to flag temporal columns found to be in pre-5.6.4 format (TIME, DATETIME, and TIMESTAMP columns without support for fractional seconds precision). This variable is disabled by default. If enabled, SHOW CREATE TABLE output looks like this:

    Press CTRL+C to copy
    CREATE TABLE `mytbl` ( `ts` timestamp /* 5.5 binary format */ NOT NULL DEFAULT CURRENT_TIMESTAMP, `dt` datetime /* 5.5 binary format */ DEFAULT NULL, `t` time /* 5.5 binary format */ DEFAULT NULL ) DEFAULT CHARSET=utf8mb4

    Output for the COLUMN_TYPE column of the Information Schema COLUMNS table is affected similarly.

    This variable is deprecated and subject to removal in a future MySQL release.

    As of MySQL 8.0.27, setting the session value of this system variable is a restricted operation. The session user must have privileges sufficient to set restricted session variables. See Section 5.1.9.1, 鈥淪ystem Variable Privileges鈥?/a>.

  • skip_external_locking

    Command-Line Format --skip-external-locking[={OFF|ON}]
    System Variable skip_external_locking
    Scope Global
    Dynamic No
    SET_VAR Hint Applies No
    Type Boolean
    Default Value ON

    This is OFF if mysqld uses external locking (system locking), ON if external locking is disabled. This affects only MyISAM table access.

    This variable is set by the --external-locking or --skip-external-locking option. External locking is disabled by default.

    External locking affects only MyISAM table access. For more information, including conditions under which it can and cannot be used, see Section 8.11.5, 鈥淓xternal Locking鈥?/a>.

  • skip_name_resolve

    Command-Line Format --skip-name-resolve[={OFF|ON}]
    System Variable skip_name_resolve
    Scope Global
    Dynamic No
    SET_VAR Hint Applies No
    Type Boolean
    Default Value OFF

    Whether to resolve host names when checking client connections. If this variable is OFF, mysqld resolves host names when checking client connections. If it is ON, mysqld uses only IP numbers; in this case, all Host column values in the grant tables must be IP addresses. See Section 5.1.12.3, 鈥淒NS Lookups and the Host Cache鈥?/a>.

    Depending on the network configuration of your system and the Host values for your accounts, clients may need to connect using an explicit --host option, such as --host=127.0.0.1 or --host=::1.

    An attempt to connect to the host 127.0.0.1 normally resolves to the localhost account. However, this fails if the server is run with skip_name_resolve enabled. If you plan to do that, make sure an account exists that can accept a connection. For example, to be able to connect as root using --host=127.0.0.1 or --host=::1, create these accounts:

    Press CTRL+C to copy
    CREATE USER 'root'@'127.0.0.1' IDENTIFIED BY 'root-password'; CREATE USER 'root'@'::1' IDENTIFIED BY 'root-password';
  • skip_networking

    Command-Line Format --skip-networking[={OFF|ON}]
    System Variable skip_networking
    Scope Global
    Dynamic No
    SET_VAR Hint Applies No
    Type Boolean
    Default Value OFF

    This variable controls whether the server permits TCP/IP connections. By default, it is disabled (permit TCP connections). If enabled, the server permits only local (non-TCP/IP) connections and all interaction with mysqld must be made using named pipes or shared memory (on Windows) or Unix socket files (on Unix). This option is highly recommended for systems where only local clients are permitted. See Section 5.1.12.3, 鈥淒NS Lookups and the Host Cache鈥?/a>.

    Because starting the server with --skip-grant-tables disables authentication checks, the server also disables remote connections in that case by enabling skip_networking.

  • skip_show_database

    Command-Line Format --skip-show-database
    System Variable skip_show_database
    Scope Global
    Dynamic No
    SET_VAR Hint Applies No
    Type Boolean
    Default Value OFF

    This prevents people from using the SHOW DATABASES statement if they do not have the SHOW DATABASES privilege. This can improve security if you have concerns about users being able to see databases belonging to other users. Its effect depends on the SHOW DATABASES privilege: If the variable value is ON, the SHOW DATABASES statement is permitted only to users who have the SHOW DATABASES privilege, and the statement displays all database names. If the value is OFF, SHOW DATABASES is permitted to all users, but displays the names of only those databases for which the user has the SHOW DATABASES or other privilege.

    Caution

    Because any static global privilege is considered a privilege for all databases, any static global privilege enables a user to see all database names with SHOW DATABASES or by examining the SCHEMATA table of INFORMATION_SCHEMA, except databases that have been restricted at the database level by partial revokes.

  • slow_launch_time

    Command-Line Format --slow-launch-time=#
    System Variable slow_launch_time
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Integer
    Default Value 2
    Minimum Value 0
    Maximum Value 31536000
    Unit seconds

    If creating a thread takes longer than this many seconds, the server increments the Slow_launch_threads status variable.

  • slow_query_log

    Command-Line Format --slow-query-log[={OFF|ON}]
    System Variable slow_query_log
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Boolean
    Default Value OFF

    Whether the slow query log is enabled. The value can be 0 (or OFF) to disable the log or 1 (or ON) to enable the log. The destination for log output is controlled by the log_output system variable; if that value is NONE, no log entries are written even if the log is enabled.

    鈥?span class="quote">Slow鈥?/span> is determined by the value of the long_query_time variable. See Section 5.4.5, 鈥淭he Slow Query Log鈥?/a>.

  • slow_query_log_file

    Command-Line Format --slow-query-log-file=file_name
    System Variable slow_query_log_file
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type File name
    Default Value host_name-slow.log

    The name of the slow query log file. The default value is host_name-slow.log, but the initial value can be changed with the --slow_query_log_file option.

  • socket

    Command-Line Format --socket={file_name|pipe_name}
    System Variable socket
    Scope Global
    Dynamic No
    SET_VAR Hint Applies No
    Type String
    Default Value (Windows) MySQL
    Default Value (Other) /tmp/mysql.sock

    On Unix platforms, this variable is the name of the socket file that is used for local client connections. The default is /tmp/mysql.sock. (For some distribution formats, the directory might be different, such as /var/lib/mysql for RPMs.)

    On Windows, this variable is the name of the named pipe that is used for local client connections. The default value is MySQL (not case-sensitive).

  • sort_buffer_size

    Command-Line Format --sort-buffer-size=#
    System Variable sort_buffer_size
    Scope Global, Session
    Dynamic Yes
    SET_VAR Hint Applies Yes
    Type Integer
    Default Value 262144
    Minimum Value 32768
    Maximum Value (Windows) 4294967295
    Maximum Value (Other, 64-bit platforms) 18446744073709551615
    Maximum Value (Other, 32-bit platforms) 4294967295
    Unit bytes

    Each session that must perform a sort allocates a buffer of this size. sort_buffer_size is not specific to any storage engine and applies in a general manner for optimization. At minimum the sort_buffer_size value must be large enough to accommodate fifteen tuples in the sort buffer. Also, increasing the value of max_sort_length may require increasing the value of sort_buffer_size. For more information, see Section 8.2.1.16, 鈥淥RDER BY Optimization鈥?/a>

    If you see many Sort_merge_passes per second in SHOW GLOBAL STATUS output, you can consider increasing the sort_buffer_size value to speed up ORDER BY or GROUP BY operations that cannot be improved with query optimization or improved indexing.

    The optimizer tries to work out how much space is needed but can allocate more, up to the limit. Setting it larger than required globally slows down most queries that perform sorts. It is best to increase it as a session setting, and only for the sessions that need a larger size. On Linux, there are thresholds of 256KB and 2MB where larger values may significantly slow down memory allocation, so you should consider staying below one of those values. Experiment to find the best value for your workload. See Section B.3.3.5, 鈥淲here MySQL Stores Temporary Files鈥?/a>.

    The maximum permissible setting for sort_buffer_size is 4GB鈭?. Larger values are permitted for 64-bit platforms (except 64-bit Windows, for which large values are truncated to 4GB鈭? with a warning).

  • sql_auto_is_null

    System Variable sql_auto_is_null
    Scope Global, Session
    Dynamic Yes
    SET_VAR Hint Applies Yes
    Type Boolean
    Default Value OFF

    If this variable is enabled, then after a statement that successfully inserts an automatically generated AUTO_INCREMENT value, you can find that value by issuing a statement of the following form:

    Press CTRL+C to copy
    SELECT * FROM tbl_name WHERE auto_col IS NULL

    If the statement returns a row, the value returned is the same as if you invoked the LAST_INSERT_ID() function. For details, including the return value after a multiple-row insert, see Section 12.16, 鈥淚nformation Functions鈥?/a>. If no AUTO_INCREMENT value was successfully inserted, the SELECT statement returns no row.

    The behavior of retrieving an AUTO_INCREMENT value by using an IS NULL comparison is used by some ODBC programs, such as Access. See Obtaining Auto-Increment Values. This behavior can be disabled by setting sql_auto_is_null to OFF.

    Prior to MySQL 8.0.16, the transformation of WHERE auto_col IS NULL to WHERE auto_col = LAST_INSERT_ID() was performed only when the statement was executed, so that the value of sql_auto_is_null during execution determined whether the query was transformed. In MySQL 8.0.16 and later, the transformation is performed during statement preparation.

    The default value of sql_auto_is_null is OFF.

  • sql_big_selects

    System Variable sql_big_selects
    Scope Global, Session
    Dynamic Yes
    SET_VAR Hint Applies Yes
    Type Boolean
    Default Value ON

    If set to OFF, MySQL aborts SELECT statements that are likely to take a very long time to execute (that is, statements for which the optimizer estimates that the number of examined rows exceeds the value of max_join_size). This is useful when an inadvisable WHERE statement has been issued. The default value for a new connection is ON, which permits all SELECT statements.

    If you set the max_join_size system variable to a value other than DEFAULT, sql_big_selects is set to OFF.

  • sql_buffer_result

    System Variable sql_buffer_result
    Scope Global, Session
    Dynamic Yes
    SET_VAR Hint Applies Yes
    Type Boolean
    Default Value OFF

    If enabled, sql_buffer_result forces results from SELECT statements to be put into temporary tables. This helps MySQL free the table locks early and can be beneficial in cases where it takes a long time to send results to the client. The default value is OFF.

  • sql_generate_invisible_primary_key

    Command-Line Format --sql-generate-invisible-primary-key[={OFF|ON}]
    Introduced 8.0.30
    System Variable sql_generate_invisible_primary_key
    Scope Global, Session
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Boolean
    Default Value OFF

    Whether this server adds a generated invisible primary key to any InnoDB table that is created without one.

    This variable is not replicated. In addition, even if set on the replica, it is ignored by replication applier threads; this means that, by default, a replica does not generate a primary key for any replicated table which, on the source, was created without one. In MySQL 8.0.32 and later, you can cause the replica to generate invisible primary keys for such tables by setting REQUIRE_TABLE_PRIMARY_KEY_CHECK = GENERATE as part of a CHANGE REPLICATION SOURCE TO statement, optionally specifying a replication channel.

    For more information and examples, see Section 13.1.20.11, 鈥淕enerated Invisible Primary Keys鈥?/a>.

  • sql_log_off

    System Variable sql_log_off
    Scope Global, Session
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Boolean
    Default Value OFF
    Valid Values

    OFF (enable logging)

    ON (disable logging)

    This variable controls whether logging to the general query log is disabled for the current session (assuming that the general query log itself is enabled). The default value is OFF (that is, enable logging). To disable or enable general query logging for the current session, set the session sql_log_off variable to ON or OFF.

    Setting the session value of this system variable is a restricted operation. The session user must have privileges sufficient to set restricted session variables. See Section 5.1.9.1, 鈥淪ystem Variable Privileges鈥?/a>.

  • sql_mode

    Command-Line Format --sql-mode=name
    System Variable sql_mode
    Scope Global, Session
    Dynamic Yes
    SET_VAR Hint Applies Yes
    Type Set
    Default Value ONLY_FULL_GROUP_BY STRICT_TRANS_TABLES NO_ZERO_IN_DATE NO_ZERO_DATE ERROR_FOR_DIVISION_BY_ZERO NO_ENGINE_SUBSTITUTION
    Valid Values

    ALLOW_INVALID_DATES

    ANSI_QUOTES

    ERROR_FOR_DIVISION_BY_ZERO

    HIGH_NOT_PRECEDENCE

    IGNORE_SPACE

    NO_AUTO_VALUE_ON_ZERO

    NO_BACKSLASH_ESCAPES

    NO_DIR_IN_CREATE

    NO_ENGINE_SUBSTITUTION

    NO_UNSIGNED_SUBTRACTION

    NO_ZERO_DATE

    NO_ZERO_IN_DATE

    ONLY_FULL_GROUP_BY

    PAD_CHAR_TO_FULL_LENGTH

    PIPES_AS_CONCAT

    REAL_AS_FLOAT

    STRICT_ALL_TABLES

    STRICT_TRANS_TABLES

    TIME_TRUNCATE_FRACTIONAL

    The current server SQL mode, which can be set dynamically. For details, see Section 5.1.11, 鈥淪erver SQL Modes鈥?/a>.

    Note

    MySQL installation programs may configure the SQL mode during the installation process.

    If the SQL mode differs from the default or from what you expect, check for a setting in an option file that the server reads at startup.

  • sql_notes

    System Variable sql_notes
    Scope Global, Session
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Boolean
    Default Value ON

    If enabled (the default), diagnostics of Note level increment warning_count and the server records them. If disabled, Note diagnostics do not increment warning_count and the server does not record them. mysqldump includes output to disable this variable so that reloading the dump file does not produce warnings for events that do not affect the integrity of the reload operation.

  • sql_quote_show_create

    System Variable sql_quote_show_create
    Scope Global, Session
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Boolean
    Default Value ON

    If enabled (the default), the server quotes identifiers for SHOW CREATE TABLE and SHOW CREATE DATABASE statements. If disabled, quoting is disabled. This option is enabled by default so that replication works for identifiers that require quoting. See Section 13.7.7.10, 鈥淪HOW CREATE TABLE Statement鈥?/a>, and Section 13.7.7.6, 鈥淪HOW CREATE DATABASE Statement鈥?/a>.

  • sql_require_primary_key

    Command-Line Format --sql-require-primary-key[={OFF|ON}]
    Introduced 8.0.13
    System Variable sql_require_primary_key
    Scope Global, Session
    Dynamic Yes
    SET_VAR Hint Applies Yes
    Type Boolean
    Default Value OFF

    Whether statements that create new tables or alter the structure of existing tables enforce the requirement that tables have a primary key.

    Setting the session value of this system variable is a restricted operation. The session user must have privileges sufficient to set restricted session variables. See Section 5.1.9.1, 鈥淪ystem Variable Privileges鈥?/a>.

    Enabling this variable helps avoid performance problems in row-based replication that can occur when tables have no primary key. Suppose that a table has no primary key and an update or delete modifies multiple rows. On the replication source server, this operation can be performed using a single table scan but, when replicated using row-based replication, results in a table scan for each row to be modified on the replica. With a primary key, these table scans do not occur.

    sql_require_primary_key applies to both base tables and TEMPORARY tables, and changes to its value are replicated to replica servers. As of MySQL 8.0.18, it applies only to storage engines that can participate in replication.

    When enabled, sql_require_primary_key has these effects:

    • Attempts to create a new table with no primary key fail with an error. This includes CREATE TABLE ... LIKE. It also includes CREATE TABLE ... SELECT, unless the CREATE TABLE part includes a primary key definition.

    • Attempts to drop the primary key from an existing table fail with an error, with the exception that dropping the primary key and adding a primary key in the same ALTER TABLE statement is permitted.

      Dropping the primary key fails even if the table also contains a UNIQUE NOT NULL index.

    • Attempts to import a table with no primary key fail with an error.

    The REQUIRE_TABLE_PRIMARY_KEY_CHECK option of the CHANGE REPLICATION SOURCE TO statement (MySQL 8.0.23 and later) or CHANGE MASTER TO statement (before MySQL 8.0.23) enables a replica to select its own policy for primary key checks. When the option is set to ON for a replication channel, the replica always uses the value ON for the sql_require_primary_key system variable in replication operations, requiring a primary key. When the option is set to OFF, the replica always uses the value OFF for the sql_require_primary_key system variable in replication operations, so that a primary key is never required, even if the source required one. When the REQUIRE_TABLE_PRIMARY_KEY_CHECK option is set to STREAM, which is the default, the replica uses whatever value is replicated from the source for each transaction. With the STREAM setting for the REQUIRE_TABLE_PRIMARY_KEY_CHECK option, if privilege checks are in use for the replication channel, the PRIVILEGE_CHECKS_USER account needs privileges sufficient to set restricted session variables, so that it can set the session value for the sql_require_primary_key system variable. With the ON or OFF settings, the account does not need these privileges. For more information, see Section 17.3.3, 鈥淩eplication Privilege Checks鈥?/a>.

  • sql_safe_updates

    System Variable sql_safe_updates
    Scope Global, Session
    Dynamic Yes
    SET_VAR Hint Applies Yes
    Type Boolean
    Default Value OFF

    If this variable is enabled, UPDATE and DELETE statements that do not use a key in the WHERE clause or a LIMIT clause produce an error. This makes it possible to catch UPDATE and DELETE statements where keys are not used properly and that would probably change or delete a large number of rows. The default value is OFF.

    For the mysql client, sql_safe_updates can be enabled by using the --safe-updates option. For more information, see Using Safe-Updates Mode (--safe-updates).

  • sql_select_limit

    System Variable sql_select_limit
    Scope Global, Session
    Dynamic Yes
    SET_VAR Hint Applies Yes
    Type Integer
    Default Value 18446744073709551615
    Minimum Value 0
    Maximum Value 18446744073709551615

    The maximum number of rows to return from SELECT statements. For more information, see Using Safe-Updates Mode (--safe-updates).

    The default value for a new connection is the maximum number of rows that the server permits per table. Typical default values are (232)鈭? or (264)鈭?. If you have changed the limit, the default value can be restored by assigning a value of DEFAULT.

    If a SELECT has a LIMIT clause, the LIMIT takes precedence over the value of sql_select_limit.

  • sql_warnings

    System Variable sql_warnings
    Scope Global, Session
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Boolean
    Default Value OFF

    This variable controls whether single-row INSERT statements produce an information string if warnings occur. The default is OFF. Set the value to ON to produce an information string.

  • ssl_ca

    Command-Line Format --ssl-ca=file_name
    System Variable ssl_ca
    Scope Global
    Dynamic (鈮?8.0.16) Yes
    Dynamic (鈮?8.0.15) No
    SET_VAR Hint Applies No
    Type File name
    Default Value NULL

    The path name of the Certificate Authority (CA) certificate file in PEM format. The file contains a list of trusted SSL Certificate Authorities.

    As of MySQL 8.0.16, this variable is dynamic and can be modified at runtime to affect the TLS context the server uses for new connections. See Server-Side Runtime Configuration and Monitoring for Encrypted Connections. Prior to MySQL 8.0.16, this variable can be set only at server startup.

  • ssl_capath

    Command-Line Format --ssl-capath=dir_name
    System Variable ssl_capath
    Scope Global
    Dynamic (鈮?8.0.16) Yes
    Dynamic (鈮?8.0.15) No
    SET_VAR Hint Applies No
    Type Directory name
    Default Value NULL

    The path name of the directory that contains trusted SSL Certificate Authority (CA) certificate files in PEM format.

    As of MySQL 8.0.16, this variable is dynamic and can be modified at runtime to affect the TSL context the server uses for new connections. See Server-Side Runtime Configuration and Monitoring for Encrypted Connections. Prior to MySQL 8.0.16, this variable can be set only at server startup.

  • ssl_cert

    Command-Line Format --ssl-cert=file_name
    System Variable ssl_cert
    Scope Global
    Dynamic (鈮?8.0.16) Yes
    Dynamic (鈮?8.0.15) No
    SET_VAR Hint Applies No
    Type File name
    Default Value NULL

    The path name of the server SSL public key certificate file in PEM format.

    If the server is started with ssl_cert set to a certificate that uses any restricted cipher or cipher category, the server starts with support for encrypted connections disabled. For information about cipher restrictions, see Connection Cipher Configuration.

    As of MySQL 8.0.16, this variable is dynamic and can be modified at runtime to affect the TSL context the server uses for new connections. See Server-Side Runtime Configuration and Monitoring for Encrypted Connections. Prior to MySQL 8.0.16, this variable can be set only at server startup.

    Note

    Chained SSL certificate support was added in v8.0.30; previously only the first certificate was read.

  • ssl_cipher

    Command-Line Format --ssl-cipher=name
    System Variable ssl_cipher
    Scope Global
    Dynamic (鈮?8.0.16) Yes
    Dynamic (鈮?8.0.15) No
    SET_VAR Hint Applies No
    Type String
    Default Value NULL

    The list of permissible encryption ciphers for connections that use TLS protocols up through TLSv1.2. If no cipher in the list is supported, encrypted connections that use these TLS protocols do not work.

    For greatest portability, the cipher list should be a list of one or more cipher names, separated by colons. The following example shows two cipher names separated by a colon:

    Press CTRL+C to copy
    [mysqld] ssl_cipher="DHE-RSA-AES128-GCM-SHA256:AES128-SHA"

    OpenSSL supports the syntax for specifying ciphers described in the OpenSSL documentation at https://www.openssl.org/docs/manmaster/man1/ciphers.html.

    For information about which encryption ciphers MySQL supports, see Section 6.3.2, 鈥淓ncrypted Connection TLS Protocols and Ciphers鈥?/a>.

    As of MySQL 8.0.16, this variable is dynamic and can be modified at runtime to affect the TSL context the server uses for new connections. See Server-Side Runtime Configuration and Monitoring for Encrypted Connections. Prior to MySQL 8.0.16, this variable can be set only at server startup.

  • ssl_crl

    Command-Line Format --ssl-crl=file_name
    System Variable ssl_crl
    Scope Global
    Dynamic (鈮?8.0.16) Yes
    Dynamic (鈮?8.0.15) No
    SET_VAR Hint Applies No
    Type File name
    Default Value NULL

    The path name of the file containing certificate revocation lists in PEM format.

    As of MySQL 8.0.16, this variable is dynamic and can be modified at runtime to affect the TSL context the server uses for new connections. See Server-Side Runtime Configuration and Monitoring for Encrypted Connections. Prior to MySQL 8.0.16, this variable can be set only at server startup.

  • ssl_crlpath

    Command-Line Format --ssl-crlpath=dir_name
    System Variable ssl_crlpath
    Scope Global
    Dynamic (鈮?8.0.16) Yes
    Dynamic (鈮?8.0.15) No
    SET_VAR Hint Applies No
    Type Directory name
    Default Value NULL

    The path of the directory that contains certificate revocation-list files in PEM format.

    As of MySQL 8.0.16, this variable is dynamic and can be modified at runtime to affect the TSL context the server uses for new connections. See Server-Side Runtime Configuration and Monitoring for Encrypted Connections. Prior to MySQL 8.0.16, this variable can be set only at server startup.

  • ssl_fips_mode

    Command-Line Format --ssl-fips-mode={OFF|ON|STRICT}
    System Variable ssl_fips_mode
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Enumeration
    Default Value OFF
    Valid Values

    OFF (or 0)

    ON (or 1)

    STRICT (or 2)

    Controls whether to enable FIPS mode on the server side. The ssl_fips_mode system variable differs from other ssl_xxx system variables in that it is not used to control whether the server permits encrypted connections, but rather to affect which cryptographic operations are permitted. See Section 6.8, 鈥淔IPS Support鈥?/a>.

    These ssl_fips_mode values are permitted:

    • OFF (or 0): Disable FIPS mode.

    • ON (or 1): Enable FIPS mode.

    • STRICT (or 2): Enable 鈥?span class="quote">strict鈥?/span> FIPS mode.

    Note

    If the OpenSSL FIPS Object Module is not available, the only permitted value for ssl_fips_mode is OFF. In this case, setting ssl_fips_mode to ON or STRICT at startup causes the server to produce an error message and exit.

  • ssl_key

    Command-Line Format --ssl-key=file_name
    System Variable ssl_key
    Scope Global
    Dynamic (鈮?8.0.16) Yes
    Dynamic (鈮?8.0.15) No
    SET_VAR Hint Applies No
    Type File name
    Default Value NULL

    The path name of the server SSL private key file in PEM format. For better security, use a certificate with an RSA key size of at least 2048 bits.

    If the key file is protected by a passphrase, the server prompts the user for the passphrase. The password must be given interactively; it cannot be stored in a file. If the passphrase is incorrect, the program continues as if it could not read the key.

    As of MySQL 8.0.16, this variable is dynamic and can be modified at runtime to affect the TSL context the server uses for new connections. See Server-Side Runtime Configuration and Monitoring for Encrypted Connections. Prior to MySQL 8.0.16, this variable can be set only at server startup.

  • ssl_session_cache_mode

    Command-Line Format --ssl_session_cache_mode={ON|OFF}
    Introduced 8.0.29
    System Variable ssl_session_cache_mode
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Boolean
    Default Value ON
    Valid Values

    ON

    OFF

    Controls whether to enable the session cache in memory on the server side and session-ticket generation by the server. The default mode is ON (enable session cache mode). A change to the ssl_session_cache_mode system variable has an effect only after the ALTER INSTANCE RELOAD TLS statement has been executed, or after a restart if the variable value was persisted.

    These ssl_session_cache_mode values are permitted:

    • ON: Enable session cache mode.

    • OFF: Disable session cache mode.

    The server does not advertise its support for session resumption if the value of this system variable is OFF. When running on OpenSSL 1.0.x the session tickets are always generated, but the tickets are not usable when ssl_session_cache_mode is enabled.

    The current value in effect for ssl_session_cache_mode can be observed with the Ssl_session_cache_mode status variable.

  • ssl_session_cache_timeout

    Command-Line Format --ssl_session_cache_timeout
    Introduced 8.0.29
    System Variable ssl_session_cache_timeout
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Integer
    Default Value 300
    Minimum Value 0
    Maximum Value 84600
    Unit seconds

    Sets a period of time during which prior session reuse is permitted when establishing a new encrypted connection to the server, provided the ssl_session_cache_mode system variable is enabled and prior session data is available. If the session timeout expires, a session can no longer be reused.

    The default value is 300 seconds and the maximum value is 84600 (or one day in seconds). A change to the ssl_session_cache_timeout system variable has an effect only after the ALTER INSTANCE RELOAD TLS statement has been executed, or after a restart if the variable value was persisted. The current value in effect for ssl_session_cache_timeout can be observed with the Ssl_session_cache_timeout status variable.

  • stored_program_cache

    Command-Line Format --stored-program-cache=#
    System Variable stored_program_cache
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Integer
    Default Value 256
    Minimum Value 16
    Maximum Value 524288

    Sets a soft upper limit for the number of cached stored routines per connection. The value of this variable is specified in terms of the number of stored routines held in each of the two caches maintained by the MySQL Server for, respectively, stored procedures and stored functions.

    Whenever a stored routine is executed this cache size is checked before the first or top-level statement in the routine is parsed; if the number of routines of the same type (stored procedures or stored functions according to which is being executed) exceeds the limit specified by this variable, the corresponding cache is flushed and memory previously allocated for cached objects is freed. This allows the cache to be flushed safely, even when there are dependencies between stored routines.

    The stored procedure and stored function caches exists in parallel with the stored program definition cache partition of the dictionary object cache. The stored procedure and stored function caches are per connection, while the stored program definition cache is shared. The existence of objects in the stored procedure and stored function caches have no dependence on the existence of objects in the stored program definition cache, and vice versa. For more information, see Section 14.4, 鈥淒ictionary Object Cache鈥?/a>.

  • stored_program_definition_cache

    Command-Line Format --stored-program-definition-cache=#
    System Variable stored_program_definition_cache
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Integer
    Default Value 256
    Minimum Value 256
    Maximum Value 524288

    Defines a limit for the number of stored program definition objects, both used and unused, that can be kept in the dictionary object cache.

    Unused stored program definition objects are only kept in the dictionary object cache when the number in use is less than the capacity defined by stored_program_definition_cache.

    A setting of 0 means that stored program definition objects are only kept in the dictionary object cache while they are in use.

    The stored program definition cache partition exists in parallel with the stored procedure and stored function caches that are configured using the stored_program_cache option.

    The stored_program_cache option sets a soft upper limit for the number of cached stored procedures or functions per connection, and the limit is checked each time a connection executes a stored procedure or function. The stored program definition cache partition, on the other hand, is a shared cache that stores stored program definition objects for other purposes. The existence of objects in the stored program definition cache partition has no dependence on the existence of objects in the stored procedure cache or stored function cache, and vice versa.

    For related information, see Section 14.4, 鈥淒ictionary Object Cache鈥?/a>.

  • super_read_only

    Command-Line Format --super-read-only[={OFF|ON}]
    System Variable super_read_only
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Boolean
    Default Value OFF

    If the read_only system variable is enabled, the server permits no client updates except from users who have the CONNECTION_ADMIN privilege (or the deprecated SUPER privilege). If the super_read_only system variable is also enabled, the server prohibits client updates even from users who have CONNECTION_ADMIN or SUPER. See the description of the read_only system variable for a description of read-only mode and information about how read_only and super_read_only interact.

    Client updates prevented when super_read_only is enabled include operations that do not necessarily appear to be updates, such as CREATE FUNCTION (to install a loadable function), INSTALL PLUGIN, and INSTALL COMPONENT. These operations are prohibited because they involve changes to tables in the mysql system schema.

    Similarly, if the Event Scheduler is enabled, enabling the super_read_only system variable prevents it from updating event 鈥?span class="quote">last executed鈥?/span> timestamps in the events data dictionary table. This causes the Event Scheduler to stop the next time it tries to execute a scheduled event, after writing a message to the server error log. (In this situation the event_scheduler system variable does not change from ON to OFF. An implication is that this variable rejects the DBA intent that the Event Scheduler be enabled or disabled, where its actual status of started or stopped may be distinct.). If super_read_only is subsequently disabled after being enabled, the server automatically restarts the Event Scheduler as needed, as of MySQL 8.0.26. Prior to MySQL 8.0.26, it is necessary to manually restart the Event Scheduler by enabling it again.

    Changes to super_read_only on a replication source server are not replicated to replica servers. The value can be set on a replica independent of the setting on the source.

  • syseventlog.facility

    Command-Line Format --syseventlog.facility=value
    Introduced 8.0.13
    System Variable syseventlog.facility
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type String
    Default Value daemon

    The facility for error log output written to syslog (what type of program is sending the message). This variable is unavailable unless the log_sink_syseventlog error log component is installed. See Section 5.4.2.8, 鈥淓rror Logging to the System Log鈥?/a>.

    The permitted values can vary per operating system; consult your system syslog documentation.

    This variable does not exist on Windows.

  • syseventlog.include_pid

    Command-Line Format --syseventlog.include-pid[={OFF|ON}]
    Introduced 8.0.13
    System Variable syseventlog.include_pid
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Boolean
    Default Value ON

    Whether to include the server process ID in each line of error log output written to syslog. This variable is unavailable unless the log_sink_syseventlog error log component is installed. See Section 5.4.2.8, 鈥淓rror Logging to the System Log鈥?/a>.

    This variable does not exist on Windows.

  • syseventlog.tag

    Command-Line Format --syseventlog.tag=tag
    Introduced 8.0.13
    System Variable syseventlog.tag
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type String
    Default Value empty string

    The tag to be added to the server identifier in error log output written to syslog or the Windows Event Log. This variable is unavailable unless the log_sink_syseventlog error log component is installed. See Section 5.4.2.8, 鈥淓rror Logging to the System Log鈥?/a>.

    By default, no tag is set, so the server identifier is simply MySQL on Windows, and mysqld on other platforms. If a tag value of tag is specified, it is appended to the server identifier with a leading hyphen, resulting in a syslog identifier of mysqld-tag (or MySQL-tag on Windows).

    On Windows, to use a tag that does not already exist, the server must be run from an account with Administrator privileges, to permit creation of a registry entry for the tag. Elevated privileges are not required if the tag already exists.

  • system_time_zone

    System Variable system_time_zone
    Scope Global
    Dynamic No
    SET_VAR Hint Applies No
    Type String

    The server system time zone. When the server begins executing, it inherits a time zone setting from the machine defaults, possibly modified by the environment of the account used for running the server or the startup script. The value is used to set system_time_zone. To explicitly specify the system time zone, set the TZ environment variable or use the --timezone option of the mysqld_safe script.

    As of MySQL 8.0.26, in addition to startup time initialization, if the server host time zone changes (for example, due to daylight saving time), system_time_zone reflects that change, which has these implications for applications:

    • Queries that reference system_time_zone will get one value before a daylight saving change and a different value after the change.

    • For queries that begin executing before a daylight saving change and end after the change, the system_time_zone remains constant within the query because the value is usually cached at the beginning of execution.

    The system_time_zone variable differs from the time_zone variable. Although they might have the same value, the latter variable is used to initialize the time zone for each client that connects. See Section 5.1.15, 鈥淢ySQL Server Time Zone Support鈥?/a>.

  • table_definition_cache

    Command-Line Format --table-definition-cache=#
    System Variable table_definition_cache
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Integer
    Default Value -1 (signifies autosizing; do not assign this literal value)
    Minimum Value 400
    Maximum Value 524288

    The number of table definitions that can be stored in the table definition cache. If you use a large number of tables, you can create a large table definition cache to speed up opening of tables. The table definition cache takes less space and does not use file descriptors, unlike the normal table cache. The minimum value is 400. The default value is based on the following formula, capped to a limit of 2000:

    Press CTRL+C to copy
    MIN(400 + table_open_cache / 2, 2000)

    For InnoDB, the table_definition_cache setting acts as a soft limit for the number of table instances in the dictionary object cache and the number file-per-table tablespaces that can be open at one time.

    If the number of table instances in the dictionary object cache exceeds the table_definition_cache limit, an LRU mechanism begins marking table instances for eviction and eventually removes them from the dictionary object cache. The number of open tables with cached metadata can be higher than the table_definition_cache limit due to table instances with foreign key relationships, which are not placed on the LRU list.

    The number of file-per-table tablespaces that can be open at one time is limited by both the table_definition_cache and innodb_open_files settings. If both variables are set, the highest setting is used. If neither variable is set, the table_definition_cache setting, which has a higher default value, is used. If the number of open tablespaces exceeds the limit defined by table_definition_cache or innodb_open_files, an LRU mechanism searches the LRU list for tablespace files that are fully flushed and not currently being extended. This process is performed each time a new tablespace is opened. Only inactive tablespaces are closed.

    The table definition cache exists in parallel with the table definition cache partition of the dictionary object cache. Both caches store table definitions but serve different parts of the MySQL server. Objects in one cache have no dependence on the existence of objects in the other. For more information, see Section 14.4, 鈥淒ictionary Object Cache鈥?/a>.

  • table_encryption_privilege_check

    Command-Line Format --table-encryption-privilege-check[={OFF|ON}]
    Introduced 8.0.16
    System Variable table_encryption_privilege_check
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Boolean
    Default Value OFF

    Controls the TABLE_ENCRYPTION_ADMIN privilege check that occurs when creating or altering a schema or general tablespace with encryption that differs from the default_table_encryption setting, or when creating or altering a table with an encryption setting that differs from the default schema encryption. The check is disabled by default.

    Setting table_encryption_privilege_check at runtime requires the SUPER privilege.

    table_encryption_privilege_check supports SET PERSIST and SET PERSIST_ONLY syntax. See Section 5.1.9.3, 鈥淧ersisted System Variables鈥?/a>.

    For more information, see Defining an Encryption Default for Schemas and General Tablespaces.

  • table_open_cache

    Command-Line Format --table-open-cache=#
    System Variable table_open_cache
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Integer
    Default Value 4000
    Minimum Value 1
    Maximum Value 524288

    The number of open tables for all threads. Increasing this value increases the number of file descriptors that mysqld requires. The effective value of this variable is the greater of the effective value of open_files_limit - 10 - the effective value of max_connections / 2, and 400; that is

    Press CTRL+C to copy
    MAX( (open_files_limit - 10 - max_connections) / 2, 400 )

    You can check whether you need to increase the table cache by checking the Opened_tables status variable. If the value of Opened_tables is large and you do not use FLUSH TABLES often (which just forces all tables to be closed and reopened), then you should increase the value of the table_open_cache variable. For more information about the table cache, see Section 8.4.3.1, 鈥淗ow MySQL Opens and Closes Tables鈥?/a>.

  • table_open_cache_instances

    Command-Line Format --table-open-cache-instances=#
    System Variable table_open_cache_instances
    Scope Global
    Dynamic No
    SET_VAR Hint Applies No
    Type Integer
    Default Value 16
    Minimum Value 1
    Maximum Value 64

    The number of open tables cache instances. To improve scalability by reducing contention among sessions, the open tables cache can be partitioned into several smaller cache instances of size table_open_cache / table_open_cache_instances . A session needs to lock only one instance to access it for DML statements. This segments cache access among instances, permitting higher performance for operations that use the cache when there are many sessions accessing tables. (DDL statements still require a lock on the entire cache, but such statements are much less frequent than DML statements.)

    A value of 8 or 16 is recommended on systems that routinely use 16 or more cores. However, if you have many large triggers on your tables that cause a high memory load, the default setting for table_open_cache_instances might lead to excessive memory usage. In that situation, it can be helpful to set table_open_cache_instances to 1 in order to restrict memory usage.

  • tablespace_definition_cache

    Command-Line Format --tablespace-definition-cache=#
    System Variable tablespace_definition_cache
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Integer
    Default Value 256
    Minimum Value 256
    Maximum Value 524288

    Defines a limit for the number of tablespace definition objects, both used and unused, that can be kept in the dictionary object cache.

    Unused tablespace definition objects are only kept in the dictionary object cache when the number in use is less than the capacity defined by tablespace_definition_cache.

    A setting of 0 means that tablespace definition objects are only kept in the dictionary object cache while they are in use.

    For more information, see Section 14.4, 鈥淒ictionary Object Cache鈥?/a>.

  • temptable_max_mmap

    Command-Line Format --temptable-max-mmap=#
    Introduced 8.0.23
    System Variable temptable_max_mmap
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Integer
    Default Value 1073741824
    Minimum Value 0
    Maximum Value 2^64-1
    Unit bytes

    Defines the maximum amount of memory (in bytes) the TempTable storage engine is permitted to allocate from memory-mapped temporary files before it starts storing data to InnoDB internal temporary tables on disk. A setting of 0 disables allocation of memory from memory-mapped temporary files. For more information, see Section 8.4.4, 鈥淚nternal Temporary Table Use in MySQL鈥?/a>.

  • temptable_max_ram

    Command-Line Format --temptable-max-ram=#
    System Variable temptable_max_ram
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Integer
    Default Value 1073741824
    Minimum Value 2097152
    Maximum Value 2^64-1
    Unit bytes

    Defines the maximum amount of memory that can be occupied by the TempTable storage engine before it starts storing data on disk. The default value is 1073741824 bytes (1GiB). For more information, see Section 8.4.4, 鈥淚nternal Temporary Table Use in MySQL鈥?/a>.

  • temptable_use_mmap

    Command-Line Format --temptable-use-mmap[={OFF|ON}]
    Introduced 8.0.16
    Deprecated 8.0.26
    System Variable temptable_use_mmap
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Boolean
    Default Value ON

    Defines whether the TempTable storage engine allocates space for internal in-memory temporary tables as memory-mapped temporary files when the amount of memory occupied by the TempTable storage engine exceeds the limit defined by the temptable_max_ram variable. When temptable_use_mmap is disabled, the TempTable storage engine uses InnoDB on-disk internal temporary tables instead. For more information, see Section 8.4.4, 鈥淚nternal Temporary Table Use in MySQL鈥?/a>.

  • thread_cache_size

    Command-Line Format --thread-cache-size=#
    System Variable thread_cache_size
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Integer
    Default Value -1 (signifies autosizing; do not assign this literal value)
    Minimum Value 0
    Maximum Value 16384

    How many threads the server should cache for reuse. When a client disconnects, the client's threads are put in the cache if there are fewer than thread_cache_size threads there. Requests for threads are satisfied by reusing threads taken from the cache if possible, and only when the cache is empty is a new thread created. This variable can be increased to improve performance if you have a lot of new connections. Normally, this does not provide a notable performance improvement if you have a good thread implementation. However, if your server sees hundreds of connections per second you should normally set thread_cache_size high enough so that most new connections use cached threads. By examining the difference between the Connections and Threads_created status variables, you can see how efficient the thread cache is. For details, see Section 5.1.10, 鈥淪erver Status Variables鈥?/a>.

    The default value is based on the following formula, capped to a limit of 100:

  • thread_handling

    Command-Line Format --thread-handling=name
    System Variable thread_handling
    Scope Global
    Dynamic No
    SET_VAR Hint Applies No
    Type Enumeration
    Default Value one-thread-per-connection
    Valid Values

    no-threads

    one-thread-per-connection

    loaded-dynamically

    The thread-handling model used by the server for connection threads. The permissible values are no-threads (the server uses a single thread to handle one connection), one-thread-per-connection (the server uses one thread to handle each client connection), and loaded-dynamically (set by the thread pool plugin when it initializes). no-threads is useful for debugging under Linux; see Section 5.9, 鈥淒ebugging MySQL鈥?/a>.

  • thread_pool_algorithm

    Command-Line Format --thread-pool-algorithm=#
    System Variable thread_pool_algorithm
    Scope Global
    Dynamic No
    SET_VAR Hint Applies No
    Type Integer
    Default Value 0
    Minimum Value 0
    Maximum Value 1

    This variable controls which algorithm the thread pool plugin uses:

    • A value of 0 (the default) uses a conservative low-concurrency algorithm which is most well tested and is known to produce very good results.

    • A value of 1 increases the concurrency and uses a more aggressive algorithm which at times has been known to perform 5鈥?0% better on optimal thread counts, but has degrading performance as the number of connections increases. Its use should be considered as experimental and not supported.

    This variable is available only if the thread pool plugin is enabled. See Section 5.6.3, 鈥淢ySQL Enterprise Thread Pool鈥?/a>.

  • thread_pool_dedicated_listeners

    Command-Line Format --thread-pool-dedicated-listeners
    Introduced 8.0.23
    System Variable thread_pool_dedicated_listeners
    Scope Global
    Dynamic No
    SET_VAR Hint Applies No
    Type Boolean
    Default Value OFF

    Dedicates a listener thread in each thread group to listen for incoming statements from connections assigned to the group.

    • OFF: (Default) Disables dedicated listener threads.

    • ON: Dedicates a listener thread in each thread group to listen for incoming statements from connections assigned to the group. Dedicated listener threads do not execute queries.

    Enabling thread_pool_dedicated_listeners is only useful when a transaction limit is defined by thread_pool_max_transactions_limit. Otherwise, thread_pool_dedicated_listeners should not be enabled.

    MySQL Database Service introduced this variable in MySQL 8.0.23. It is available with MySQL Enterprise Edition from MySQL 8.0.31.

  • thread_pool_high_priority_connection

    Command-Line Format --thread-pool-high-priority-connection=#
    System Variable thread_pool_high_priority_connection
    Scope Global, Session
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Integer
    Default Value 0
    Minimum Value 0
    Maximum Value 1

    This variable affects queuing of new statements prior to execution. If the value is 0 (false, the default), statement queuing uses both the low-priority and high-priority queues. If the value is 1 (true), queued statements always go to the high-priority queue.

    This variable is available only if the thread pool plugin is enabled. See Section 5.6.3, 鈥淢ySQL Enterprise Thread Pool鈥?/a>.

  • thread_pool_max_active_query_threads

    Command-Line Format --thread-pool-max-active-query-threads
    Introduced 8.0.19
    System Variable thread_pool_max_active_query_threads
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Integer
    Default Value 0
    Minimum Value 0
    Maximum Value 512

    The maximum permissible number of active (running) query threads per group. If the value is 0, the thread pool plugin uses up to as many threads as are available.

    This variable is available only if the thread pool plugin is enabled. See Section 5.6.3, 鈥淢ySQL Enterprise Thread Pool鈥?/a>.

  • thread_pool_max_transactions_limit

    Command-Line Format --thread-pool-max-transactions-limit
    Introduced 8.0.23
    System Variable thread_pool_max_transactions_limit
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Integer
    Default Value 0
    Minimum Value 0
    Maximum Value 1000000

    The maximum number of transactions permitted by the thread pool plugin. Defining a transaction limit binds a thread to a transaction until it commits, which helps stabilize throughput during high concurrency.

    The default value of 0 means that there is no transaction limit. The variable is dynamic but cannot be changed from 0 to a higher value at runtime and vice versa. A non-zero value at startup permits dynamic configuration at runtime. The CONNECTION_ADMIN privilege is required to configure thread_pool_max_transactions_limit at runtime.

    When you define a transaction limit, enabling thread_pool_dedicated_listeners creates a dedicated listener thread in each thread group. The additional dedicated listener thread consumes more resources and affects thread pool performance. thread_pool_dedicated_listeners should therefore be used cautiously.

    When the limit defined by thread_pool_max_transactions_limit has been reached, new connections appear to hang until one or more existing transactions are completed. The same occurs when attempting to start a new transaction on an existing connection. If existing connections are blocked or long-running, a privileged connection may be required to access the server to increase the limit, remove the limit, or kill running transactions. See Privileged Connections.

    MySQL Database Service introduced this variable in MySQL 8.0.23. It is available with MySQL Enterprise Edition in from MySQL 8.0.31.

  • thread_pool_max_unused_threads

    Command-Line Format --thread-pool-max-unused-threads=#
    System Variable thread_pool_max_unused_threads
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Integer
    Default Value 0
    Minimum Value 0
    Maximum Value 4096

    The maximum permitted number of unused threads in the thread pool. This variable makes it possible to limit the amount of memory used by sleeping threads.

    A value of 0 (the default) means no limit on the number of sleeping threads. A value of N where N is greater than 0 means 1 consumer thread and N鈭? reserve threads. In this case, if a thread is ready to sleep but the number of sleeping threads is already at the maximum, the thread exits rather than going to sleep.

    A sleeping thread is either sleeping as a consumer thread or a reserve thread. The thread pool permits one thread to be the consumer thread when sleeping. If a thread goes to sleep and there is no existing consumer thread, it sleeps as a consumer thread. When a thread must be woken up, a consumer thread is selected if there is one. A reserve thread is selected only when there is no consumer thread to wake up.

    This variable is available only if the thread pool plugin is enabled. See Section 5.6.3, 鈥淢ySQL Enterprise Thread Pool鈥?/a>.

  • thread_pool_prio_kickup_timer

    Command-Line Format --thread-pool-prio-kickup-timer=#
    System Variable thread_pool_prio_kickup_timer
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Integer
    Default Value 1000
    Minimum Value 0
    Maximum Value 4294967294
    Unit milliseconds

    This variable affects statements waiting for execution in the low-priority queue. The value is the number of milliseconds before a waiting statement is moved to the high-priority queue. The default is 1000 (1 second).

    This variable is available only if the thread pool plugin is enabled. See Section 5.6.3, 鈥淢ySQL Enterprise Thread Pool鈥?/a>.

  • thread_pool_query_threads_per_group

    Command-Line Format --thread-pool-query-threads-per-group
    Introduced 8.0.31
    System Variable thread_pool_query_threads_per_group
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Integer
    Default Value 1
    Minimum Value 1
    Maximum Value 4096

    The maximum number of query threads permitted in a thread group. The maximum value is 4096, but if thread_pool_max_transactions_limit is set, thread_pool_query_threads_per_group must not exceed that value.

    The default value of 1 means there is one active query thread in each thread group, which works well for many loads. When you are using the high concurrency thread pool algorithm (thread_pool_algorithm = 1), consider increasing the value if you experience slower response times due to long-running transactions.

    The CONNECTION_ADMIN privilege is required to configure thread_pool_query_threads_per_group at runtime.

    If you decrease the value of thread_pool_query_threads_per_group at runtime, threads that are currently running user queries are allowed to complete, then moved to the reserve pool or terminated. if you increment the value at runtime and the thread group needs more threads, these are taken from the reserve pool if possible, otherwise they are created.

    This variable is available from MySQL 8.0.31 in MySQL Database Service and MySQL Enterprise Edition.

  • thread_pool_size

    Command-Line Format --thread-pool-size=#
    System Variable thread_pool_size
    Scope Global
    Dynamic No
    SET_VAR Hint Applies No
    Type Integer
    Default Value 16
    Minimum Value 1
    Maximum Value (鈮?8.0.19) 512
    Maximum Value (鈮?8.0.18) 64

    The number of thread groups in the thread pool. This is the most important parameter controlling thread pool performance. It affects how many statements can execute simultaneously. If a value outside the range of permissible values is specified, the thread pool plugin does not load and the server writes a message to the error log.

    This variable is available only if the thread pool plugin is enabled. See Section 5.6.3, 鈥淢ySQL Enterprise Thread Pool鈥?/a>.

  • thread_pool_stall_limit

    Command-Line Format --thread-pool-stall-limit=#
    System Variable thread_pool_stall_limit
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Integer
    Default Value 6
    Minimum Value 4
    Maximum Value 600
    Unit milliseconds * 10

    This variable affects executing statements. The value is the amount of time a statement has to finish after starting to execute before it becomes defined as stalled, at which point the thread pool permits the thread group to begin executing another statement. The value is measured in 10 millisecond units, so the default of 6 means 60ms. Short wait values permit threads to start more quickly. Short values are also better for avoiding deadlock situations. Long wait values are useful for workloads that include long-running statements, to avoid starting too many new statements while the current ones execute.

    This variable is available only if the thread pool plugin is enabled. See Section 5.6.3, 鈥淢ySQL Enterprise Thread Pool鈥?/a>.

  • thread_pool_transaction_delay

    Command-Line Format --thread-pool-transaction-delay
    Introduced 8.0.31
    System Variable thread_pool_transaction_delay
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Integer
    Default Value 0
    Minimum Value 0
    Maximum Value 300000

    The delay period before executing a new transaction, in milliseconds. The maximum value is 300000 (5 minutes).

    A transaction delay can be used in cases where parallel transactions affect the performance of other operations due to resource contention. For example, if parallel transactions affect index creation or an online buffer pool resizing operation, you can configure a transaction delay to reduce resource contention while those operations are running.

    Worker threads sleep for the number of milliseconds specified by thread_pool_transaction_delay before executing a new transaction.

    The thread_pool_transaction_delay setting does not affect queries issued from a privileged connection (a connection assigned to the Admin thread group). These queries are not subject to a configured transaction delay.

  • thread_stack

    Command-Line Format --thread-stack=#
    System Variable thread_stack
    Scope Global
    Dynamic No
    SET_VAR Hint Applies No
    Type Integer
    Default Value (64-bit platforms, 鈮?8.0.27) 1048576
    Default Value (64-bit platforms, 鈮?8.0.26) 286720
    Default Value (32-bit platforms, 鈮?8.0.27) 1048576
    Default Value (32-bit platforms, 鈮?8.0.26) 221184
    Minimum Value 131072
    Maximum Value (64-bit platforms) 18446744073709550592
    Maximum Value (32-bit platforms) 4294966272
    Unit bytes
    Block Size 1024

    The stack size for each thread. The default is large enough for normal operation. If the thread stack size is too small, it limits the complexity of the SQL statements that the server can handle, the recursion depth of stored procedures, and other memory-consuming actions.

    The block size is 1024. A value that is not an exact multiple of the block size is rounded down to the next lower multiple of the block size by MySQL Server before storing the value for the system variable. The parser allows values up to the maximum unsigned integer value for the platform (4294967295 or 232鈭? for a 32-bit system, 18446744073709551615 or 264鈭? for a 64-bit system) but the actual maximum is a block size lower.

  • time_zone

    System Variable time_zone
    Scope Global, Session
    Dynamic Yes
    SET_VAR Hint Applies (鈮?8.0.17) Yes
    SET_VAR Hint Applies (鈮?8.0.16) No
    Type String
    Default Value SYSTEM
    Minimum Value (鈮?8.0.19) -13:59
    Minimum Value (鈮?8.0.18) -12:59
    Maximum Value (鈮?8.0.19) +14:00
    Maximum Value (鈮?8.0.18) +13:00

    The current time zone. This variable is used to initialize the time zone for each client that connects. By default, the initial value of this is 'SYSTEM' (which means, 鈥?span class="quote">use the value of system_time_zone鈥?/span>). The value can be specified explicitly at server startup with the --default-time-zone option. See Section 5.1.15, 鈥淢ySQL Server Time Zone Support鈥?/a>.

    Note

    If set to SYSTEM, every MySQL function call that requires a time zone calculation makes a system library call to determine the current system time zone. This call may be protected by a global mutex, resulting in contention.

  • timestamp

    System Variable timestamp
    Scope Session
    Dynamic Yes
    SET_VAR Hint Applies Yes
    Type Numeric
    Default Value UNIX_TIMESTAMP()
    Minimum Value 1
    Maximum Value 2147483647

    Set the time for this client. This is used to get the original timestamp if you use the binary log to restore rows. timestamp_value should be a Unix epoch timestamp (a value like that returned by UNIX_TIMESTAMP(), not a value in 'YYYY-MM-DD hh:mm:ss' format) or DEFAULT.

    Setting timestamp to a constant value causes it to retain that value until it is changed again. Setting timestamp to DEFAULT causes its value to be the current date and time as of the time it is accessed.

    timestamp is a DOUBLE rather than BIGINT because its value includes a microseconds part. The maximum value corresponds to '2038-01-19 03:14:07' UTC, the same as for the TIMESTAMP data type.

    SET timestamp affects the value returned by NOW() but not by SYSDATE(). This means that timestamp settings in the binary log have no effect on invocations of SYSDATE(). The server can be started with the --sysdate-is-now option to cause SYSDATE() to be a synonym for NOW(), in which case SET timestamp affects both functions.

  • tls_ciphersuites

    Command-Line Format --tls-ciphersuites=ciphersuite_list
    Introduced 8.0.16
    System Variable tls_ciphersuites
    Scope Global
    Dynamic Yes
    SET_VAR Hint Applies No
    Type String
    Default Value NULL

    Which ciphersuites the server permits for encrypted connections that use TLSv1.3. The value is a list of zero or more colon-separated ciphersuite names.

    The ciphersuites that can be named for this variable depend on the SSL library used to compile MySQL. If this variable is not set, its default value is NULL, which means that the server permits the default set of ciphersuites. If the variable is set to the empty string, no ciphersuites are enabled and encrypted connections cannot be established. For more information, see Section 6.3.2, 鈥淓ncrypted Connection TLS Protocols and Ciphers鈥?/a>.

  • tls_version

    Command-Line Format --tls-version=protocol_list
    System Variable tls_version
    Scope Global
    Dynamic (鈮?8.0.16) Yes
    Dynamic (鈮?8.0.15) No
    SET_VAR Hint Applies No
    Type String
    Default Value (鈮?8.0.28) TLSv1.2,TLSv1.3
    Default Value (鈮?8.0.16, 鈮?8.0.27) TLSv1,TLSv1.1,TLSv1.2,TLSv1.3
    Default Value (鈮?8.0.15) TLSv1,TLSv1.1,TLSv1.2

    Which protocols the server permits for encrypted connections. The value is a list of one or more comma-separated protocol names, which are not case-sensitive. The protocols that can be named for this variable depend on the SSL library used to compile MySQL. Permitted protocols should be chosen such as not to leave 鈥?span class="quote">holes鈥?/span> in the list. For details, see Section 6.3.2, 鈥淓ncrypted Connection TLS Protocols and Ciphers鈥?/a>.

    As of MySQL 8.0.16, this variable is dynamic and can be modified at runtime to affect the TSL context the server uses for new connections. See Server-Side Runtime Configuration and Monitoring for Encrypted Connections. Prior to MySQL 8.0.16, this variable can be set only at server startup.

    Important
    • Support for the TLSv1 and TLSv1.1 connection protocols is removed from MySQL Server as of MySQL 8.0.28. The protocols were deprecated from MySQL 8.0.26. See Removal of Support for the TLSv1 and TLSv1.1 Protocols for more information.

    • Support for the TLSv1.3 protocol is available in MySQL Server as of MySQL 8.0.16, provided that MySQL Server was compiled using OpenSSL 1.1.1 or higher. The server checks the version of OpenSSL at startup, and if it is lower than 1.1.1, TLSv1.3 is removed from the default value for the system variable. In that case, the defaults are 鈥?span class="quote">TLSv1,TLSv1.1,TLSv1.2鈥?/span> up to and including MySQL 8.0.27, and 鈥?span class="quote">TLSv1.2鈥?/span> from MySQL 8.0.28.

  • tmp_table_size

    Command-Line Format --tmp-table-size=#
    System Variable tmp_table_size
    Scope Global, Session
    Dynamic Yes
    SET_VAR Hint Applies Yes
    Type Integer
    Default Value 16777216
    Minimum Value 1024
    Maximum Value 18446744073709551615
    Unit bytes

    Defines the maximum size of internal in-memory temporary tables created by the MEMORY storage engine and, as of MySQL 8.0.28, the TempTable storage engine. If an internal in-memory temporary table exceeds this size, it is automatically converted to an on-disk internal temporary table.

    The tmp_table_size variable does not apply to user-created MEMORY tables. User-created TempTable tables are not supported.

    When using the MEMORY storage engine for internal in-memory temporary tables, the actual size limit is the smaller of tmp_table_size and max_heap_table_size. The max_heap_table_size setting does not apply to TempTable tables.

    Increase the value of tmp_table_size (and max_heap_table_size if necessary when using the MEMORY storage engine for internal in-memory temporary tables) if you do many advanced GROUP BY queries and you have lots of memory.

    You can compare the number of internal on-disk temporary tables created to the total number of internal temporary tables created by comparing Created_tmp_disk_tables and Created_tmp_tables values.

    See also Section 8.4.4, 鈥淚nternal Temporary Table Use in MySQL鈥?/a>.

  • tmpdir

    Command-Line Format --tmpdir=dir_name
    System Variable tmpdir
    Scope Global
    Dynamic No
    SET_VAR Hint Applies No
    Type Directory name

    The path of the directory to use for creating temporary files. It might be useful if your default /tmp directory resides on a partition that is too small to hold temporary tables. This variable can be set to a list of several paths that are used in round-robin fashion. Paths should be separated by colon characters (:) on Unix and semicolon characters (;) on Windows.

    tmpdir can be a non-permanent location, such as a directory on a memory-based file system or a directory that is cleared when the server host restarts. If the MySQL server is acting as a replica, and you are using a non-permanent location for tmpdir, consider setting a different temporary directory for the replica using the replica_load_tmpdir or slave_load_tmpdir variable. For a replica, the temporary files used to replicate LOAD DATA statements are stored in this directory, so with a permanent location they can survive machine restarts, although replication can now continue after a restart if the temporary files have been removed.

    For more information about the storage location of temporary files, see Section B.3.3.5, 鈥淲here MySQL Stores Temporary Files鈥?/a>.

  • transaction_alloc_block_size

    Command-Line Format --transaction-alloc-block-size=#
    System Variable transaction_alloc_block_size
    Scope Global, Session
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Integer
    Default Value 8192
    Minimum Value 1024
    Maximum Value 131072
    Unit bytes
    Block Size 1024

    The amount in bytes by which to increase a per-transaction memory pool which needs memory. See the description of transaction_prealloc_size.

  • transaction_isolation

    Command-Line Format --transaction-isolation=name
    System Variable transaction_isolation
    Scope Global, Session
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Enumeration
    Default Value REPEATABLE-READ
    Valid Values

    READ-UNCOMMITTED

    READ-COMMITTED

    REPEATABLE-READ

    SERIALIZABLE

    The transaction isolation level. The default is REPEATABLE-READ.

    The transaction isolation level has three scopes: global, session, and next transaction. This three-scope implementation leads to some nonstandard isolation-level assignment semantics, as described later.

    To set the global transaction isolation level at startup, use the --transaction-isolation server option.

    At runtime, the isolation level can be set directly using the SET statement to assign a value to the transaction_isolation system variable, or indirectly using the SET TRANSACTION statement. If you set transaction_isolation directly to an isolation level name that contains a space, the name should be enclosed within quotation marks, with the space replaced by a dash. For example, use this SET statement to set the global value:

    Press CTRL+C to copy
    SET GLOBAL transaction_isolation = 'READ-COMMITTED';

    Setting the global transaction_isolation value sets the isolation level for all subsequent sessions. Existing sessions are unaffected.

    To set the session or next-level transaction_isolation value, use the SET statement. For most session system variables, these statements are equivalent ways to set the value:

    Press CTRL+C to copy
    SET @@SESSION.var_name = value; SET SESSION var_name = value; SET var_name = value; SET @@var_name = value;

    As mentioned previously, the transaction isolation level has a next-transaction scope, in addition to the global and session scopes. To enable the next-transaction scope to be set, SET syntax for assigning session system variable values has nonstandard semantics for transaction_isolation:

    • To set the session isolation level, use any of these syntaxes:

      Press CTRL+C to copy
      SET @@SESSION.transaction_isolation = value; SET SESSION transaction_isolation = value; SET transaction_isolation = value;

      For each of those syntaxes, these semantics apply:

      • Sets the isolation level for all subsequent transactions performed within the session.

      • Permitted within transactions, but does not affect the current ongoing transaction.

      • If executed between transactions, overrides any preceding statement that sets the next-transaction isolation level.

      • Corresponds to SET SESSION TRANSACTION ISOLATION LEVEL (with the SESSION keyword).

    • To set the next-transaction isolation level, use this syntax:

      Press CTRL+C to copy
      SET @@transaction_isolation = value;

      For that syntax, these semantics apply:

      • Sets the isolation level only for the next single transaction performed within the session.

      • Subsequent transactions revert to the session isolation level.

      • Not permitted within transactions.

      • Corresponds to SET TRANSACTION ISOLATION LEVEL (without the SESSION keyword).

    For more information about SET TRANSACTION and its relationship to the transaction_isolation system variable, see Section 13.3.7, 鈥淪ET TRANSACTION Statement鈥?/a>.

  • transaction_prealloc_size

    Command-Line Format --transaction-prealloc-size=#
    Deprecated 8.0.29
    System Variable transaction_prealloc_size
    Scope Global, Session
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Integer
    Default Value 4096
    Minimum Value 1024
    Maximum Value 131072
    Unit bytes
    Block Size 1024

    There is a per-transaction memory pool from which various transaction-related allocations take memory. The initial size of the pool in bytes is transaction_prealloc_size. For every allocation that cannot be satisfied from the pool because it has insufficient memory available, the pool is increased by transaction_alloc_block_size bytes. When the transaction ends, the pool is truncated to transaction_prealloc_size bytes. By making transaction_prealloc_size sufficiently large to contain all statements within a single transaction, you can avoid many malloc() calls.

    Beginning with MySQL 8.0.29, transaction_prealloc_size is deprecated; the initial size of the transaction memory pool is fixed, and setting this variable no longer has any effect. (The functioning of transaction_alloc_block_size is unaffected by this change.) Expect transaction_prealloc_size to be removed in a future release of MySQL.

  • transaction_read_only

    Command-Line Format --transaction-read-only[={OFF|ON}]
    System Variable transaction_read_only
    Scope Global, Session
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Boolean
    Default Value OFF

    The transaction access mode. The value can be OFF (read/write; the default) or ON (read only).

    The transaction access mode has three scopes: global, session, and next transaction. This three-scope implementation leads to some nonstandard access-mode assignment semantics, as described later.

    To set the global transaction access mode at startup, use the --transaction-read-only server option.

    At runtime, the access mode can be set directly using the SET statement to assign a value to the transaction_read_only system variable, or indirectly using the SET TRANSACTION statement. For example, use this SET statement to set the global value:

    Press CTRL+C to copy
    SET GLOBAL transaction_read_only = ON;

    Setting the global transaction_read_only value sets the access mode for all subsequent sessions. Existing sessions are unaffected.

    To set the session or next-level transaction_read_only value, use the SET statement. For most session system variables, these statements are equivalent ways to set the value:

    Press CTRL+C to copy
    SET @@SESSION.var_name = value; SET SESSION var_name = value; SET var_name = value; SET @@var_name = value;

    As mentioned previously, the transaction access mode has a next-transaction scope, in addition to the global and session scopes. To enable the next-transaction scope to be set, SET syntax for assigning session system variable values has nonstandard semantics for transaction_read_only,

    • To set the session access mode, use any of these syntaxes:

      Press CTRL+C to copy
      SET @@SESSION.transaction_read_only = value; SET SESSION transaction_read_only = value; SET transaction_read_only = value;

      For each of those syntaxes, these semantics apply:

      • Sets the access mode for all subsequent transactions performed within the session.

      • Permitted within transactions, but does not affect the current ongoing transaction.

      • If executed between transactions, overrides any preceding statement that sets the next-transaction access mode.

      • Corresponds to SET SESSION TRANSACTION {READ WRITE | READ ONLY} (with the SESSION keyword).

    • To set the next-transaction access mode, use this syntax:

      Press CTRL+C to copy
      SET @@transaction_read_only = value;

      For that syntax, these semantics apply:

      • Sets the access mode only for the next single transaction performed within the session.

      • Subsequent transactions revert to the session access mode.

      • Not permitted within transactions.

      • Corresponds to SET TRANSACTION {READ WRITE | READ ONLY} (without the SESSION keyword).

    For more information about SET TRANSACTION and its relationship to the transaction_read_only system variable, see Section 13.3.7, 鈥淪ET TRANSACTION Statement鈥?/a>.

  • unique_checks

    System Variable unique_checks
    Scope Global, Session
    Dynamic Yes
    SET_VAR Hint Applies Yes
    Type Boolean
    Default Value ON

    If set to 1 (the default), uniqueness checks for secondary indexes in InnoDB tables are performed. If set to 0, storage engines are permitted to assume that duplicate keys are not present in input data. If you know for certain that your data does not contain uniqueness violations, you can set this to 0 to speed up large table imports to InnoDB.

    Setting this variable to 0 does not require storage engines to ignore duplicate keys. An engine is still permitted to check for them and issue duplicate-key errors if it detects them.

  • updatable_views_with_limit

    Command-Line Format --updatable-views-with-limit[={OFF|ON}]
    System Variable updatable_views_with_limit
    Scope Global, Session
    Dynamic Yes
    SET_VAR Hint Applies Yes
    Type Boolean
    Default Value 1

    This variable controls whether updates to a view can be made when the view does not contain all columns of the primary key defined in the underlying table, if the update statement contains a LIMIT clause. (Such updates often are generated by GUI tools.) An update is an UPDATE or DELETE statement. Primary key here means a PRIMARY KEY, or a UNIQUE index in which no column can contain NULL.

    The variable can have two values:

    • 1 or YES: Issue a warning only (not an error message). This is the default value.

    • 0 or NO: Prohibit the update.

  • use_secondary_engine

    Introduced 8.0.13
    System Variable use_secondary_engine
    Scope Session
    Dynamic Yes
    SET_VAR Hint Applies Yes
    Type Enumeration
    Default Value ON
    Valid Values

    OFF

    ON

    FORCED

    For future use.

    Whether to execute queries using a secondary engine.

    For use with HeatWave. See MySQL HeatWave User Guide.

  • validate_password.xxx

    The validate_password component implements a set of system variables having names of the form validate_password.xxx. These variables affect password testing by that component; see Section 6.4.3.2, 鈥淧assword Validation Options and Variables鈥?/a>.

  • version

    The version number for the server. The value might also include a suffix indicating server build or configuration information. -debug indicates that the server was built with debugging support enabled.

  • version_comment

    System Variable version_comment
    Scope Global
    Dynamic No
    SET_VAR Hint Applies No
    Type String

    The CMake configuration program has a COMPILATION_COMMENT_SERVER option that permits a comment to be specified when building MySQL. This variable contains the value of that comment. (Prior to MySQL 8.0.14, version_comment is set by the COMPILATION_COMMENT option.) See Section 2.9.7, 鈥淢ySQL Source-Configuration Options鈥?/a>.

  • version_compile_machine

    System Variable version_compile_machine
    Scope Global
    Dynamic No
    SET_VAR Hint Applies No
    Type String

    The type of the server binary.

  • version_compile_os

    System Variable version_compile_os
    Scope Global
    Dynamic No
    SET_VAR Hint Applies No
    Type String

    The type of operating system on which MySQL was built.

  • version_compile_zlib

    System Variable version_compile_zlib
    Scope Global
    Dynamic No
    SET_VAR Hint Applies No
    Type String

    The version of the compiled-in zlib library.

  • wait_timeout

    Command-Line Format --wait-timeout=#
    System Variable wait_timeout
    Scope Global, Session
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Integer
    Default Value 28800
    Minimum Value 1
    Maximum Value (Windows) 2147483
    Maximum Value (Other) 31536000
    Unit seconds

    The number of seconds the server waits for activity on a noninteractive connection before closing it.

    On thread startup, the session wait_timeout value is initialized from the global wait_timeout value or from the global interactive_timeout value, depending on the type of client (as defined by the CLIENT_INTERACTIVE connect option to mysql_real_connect()). See also interactive_timeout.

  • warning_count

    The number of errors, warnings, and notes that resulted from the last statement that generated messages. This variable is read only. See Section 13.7.7.42, 鈥淪HOW WARNINGS Statement鈥?/a>.

  • windowing_use_high_precision

    Command-Line Format --windowing-use-high-precision[={OFF|ON}]
    System Variable windowing_use_high_precision
    Scope Global, Session
    Dynamic Yes
    SET_VAR Hint Applies Yes
    Type Boolean
    Default Value ON

    Whether to compute window operations without loss of precision. See Section 8.2.1.21, 鈥淲indow Function Optimization鈥?/a>.

  • xa_detach_on_prepare

    Command-Line Format --xa-detach-on-prepare[={OFF|ON}]
    Introduced 8.0.29
    System Variable xa_detach_on_prepare
    Scope Global, Session
    Dynamic Yes
    SET_VAR Hint Applies No
    Type Boolean
    Default Value ON

    When set to ON (enabled), all XA transactions are detached (disconnected) from the connection (session) as part of XA PREPARE. This means that the XA transaction can be committed or rolled back by another connection, even if the originating connection has not terminated, and this connection can start new transactions.

    Temporary tables cannot be used inside detached XA transactions.

    When this is OFF (disabled), an XA transaction is strictly associated with the same connection until the session disconnects. It is recommended that you allow it to be enabled (the default behavior) for replication.

    For more information, see Section 13.3.8.2, 鈥淴A Transaction States鈥?/a>.